Windshield glass and head-up display system

Abstract

Provided are a windshield glass and a head-up display system in which double images are suppressed even when s-polarized light and p-polarized light are mixed with light incident on the windshield glass in the head-up display. Provided is a windshield glass having an outer glass plate, a reflective layer comprising a plurality of layers, a retardation layer, an intermediate layer, and an inner glass plate, wherein the front surface retardation of the retardation layer at a wavelength of 550 nm is 280-400 nm, and the angle formed by the direction of the slow axis of the retardation layer and the vertical direction of the windshield glass is 1-20° or 91-110°.

Description

Windshield glass and head-up display systems

[0001] The present invention relates to a windshield glass having a reflective layer and a head-up display system.

[0002] Currently, there is known a head-up display or head-up display system that projects an image onto the windshield of a vehicle or the like to provide the driver or the like with various information such as a map, driving speed, and vehicle status. In a head-up display system, a virtual image containing the above-mentioned various information is projected onto the windshield glass and observed by the driver or the like. The virtual image is formed at a position outside the vehicle forward of the windshield glass. The virtual image is usually formed at a position 1000 mm or more forward of the windshield glass and closer to the outside world than the windshield glass. This allows the driver to obtain the above-mentioned various information while looking at the outside world ahead without having to move their line of sight significantly. Therefore, when using a head-up display system, it is expected that the driver will be able to drive safely while obtaining various information.

[0003] A head-up display system can be constructed by forming a reflective film on the windshield glass using a half-mirror film. Various half-mirror films that can be used in head-up display systems have been proposed.

[0004] Patent Document 1 describes a head-up display system that has a reflective layer that combines an optically anisotropic layer and an optically isotropic layer and is capable of reflecting a portion of p-polarized light.

[0005] The windshield glass that constitutes the head-up display system is required to be free from double images. In the method of Patent Document 1, the head-up display system directs p-polarized light onto the windshield glass, thereby reducing the reflectance of the windshield glass at the air interface on the outside of the vehicle, making it difficult to see double images.

[0006] International Publication No. 2021 / 200652

[0007] In an in-vehicle head-up display system, even if p-polarized light is incident on the windshield glass, s-polarized light may be mixed in due to the positioning of the mirror, etc. In some cases, the ratio of s-polarized light may be 10% or more, which can cause a problem of double images being easily visible. For this reason, it is required that double images are not visible even if s-polarized light is mixed in with the light incident on the windshield glass.

[0008] An object of the present invention is to provide a windshield glass and a head-up display system that can suppress double images when s-polarized light is included in the light incident on the windshield glass.

[0009] In the present invention, the double image is reduced by forming a reflective layer and a suitable retardation layer on the windshield glass. Specifically, this is achieved by the following means.

[0010] [1] A windshield glass comprising an outer glass plate, a reflective layer composed of multiple layers, a retardation layer, an intermediate layer, and an inner glass plate, wherein the retardation layer has a front retardation of 280 nm to 400 nm at a wavelength of 550 nm, and the angle between the direction of the slow axis of the retardation layer and the vertical direction of the windshield glass is 1° to 20° or 91° to 110°. [2] The windshield glass according to [1], wherein the retardation layer has a front retardation of 320 nm to 350 nm at a wavelength of 550 nm. [3] The windshield glass according to [1] or [2], wherein the angle between the direction of the slow axis of the retardation layer and the vertical direction of the windshield glass is 2° to 10° or 92° to 100°. [4] The windshield glass according to any one of [1] to [3], wherein the reflective layer and the retardation layer are disposed between the outer glass plate and the inner glass plate, and the retardation layer is disposed closer to the inner glass plate than the reflective layer. [5] The windshield glass according to any one of [1] to [3], wherein the reflective layer and the retardation layer are disposed between the outer glass sheet and the inner glass sheet, and the retardation layer is disposed closer to the outer glass sheet than the reflective layer. [6] The windshield glass according to any one of [1] to [3], wherein the reflective layer and the retardation layer are disposed on the surface of the inner glass sheet opposite the outer glass sheet, and the retardation layer is disposed at a position farther from the inner glass sheet than the reflective layer. [7] The windshield glass according to any one of [1] to [3], wherein the reflective layer and the retardation layer are disposed on the surface of the inner glass sheet opposite the outer glass sheet, and the retardation layer is disposed closer to the inner glass sheet than the reflective layer. [8] The windshield glass according to any one of [1] to [7], wherein the reflective layer is a reflective layer formed by laminating an inorganic layer. [9] The windshield glass according to any one of [1] to [7], wherein the reflective layer is a linearly polarized reflective layer formed by alternately laminating optically anisotropic layers and optically isotropic layers.

[10] A head-up display system comprising the windshield glass according to any one of [1] to [9] and a projector that irradiates projection light onto the inner glass plate side of the windshield glass.

[11] The head-up display system according to

[10] , wherein the projected light from the projector contains an s-polarized component and a p-polarized component, and the ratio of the s-polarized component is 10% or more and 40% or less.

[0011] According to the present invention, it is possible to provide a windshield glass and a head-up display system in which double images are suppressed even when incident light in which s-polarized components are mixed with p-polarized components is used.

[0012] FIG. 1 is a schematic diagram showing an example of a windshield glass of the present invention. FIG. 2 is a schematic diagram showing a linearly polarized reflective film as viewed from the front. FIG. 3 is a schematic diagram showing an example of a head-up display having the windshield glass of the present invention. FIG. 4 is a schematic diagram showing the s-polarized ratio of incident light. FIG. 5 is a diagram for explaining the angle of the slow axis. FIG. 6 is a schematic diagram showing another example of the windshield glass of the present invention. FIG. 7 is a schematic diagram showing another example of the windshield glass of the present invention.

[0013] The windshield glass and head-up display system of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings. The drawings described below are merely illustrative for explaining the present invention, and the present invention is not limited to these drawings. In the following, the term "to" indicating a numerical range includes the values ​​written on both sides. For example, when ε1 is between α1 and β1, the range of ε1 includes α1 and β1, and expressed in mathematical symbols, α1≦ε1≦β1. Unless otherwise specified, angles such as "angles expressed by specific numerical values," "parallel," "perpendicular," and "orthogonal" include a generally acceptable error range in the relevant technical field. Furthermore, "same" includes a generally acceptable error range in the relevant technical field, and "overall" and similar expressions also include a generally acceptable error range in the relevant technical field.

[0014] Unless otherwise specified, the term "light" refers to visible light and natural light (unpolarized). Visible light is electromagnetic light with wavelengths visible to the human eye, and typically refers to light in the wavelength range of 380 to 780 nm. Invisible light is light in the wavelength range of less than 380 nm or greater than 780 nm. Furthermore, although not limited thereto, within visible light, light in the wavelength range of 420 to 490 nm is blue (B) light, light in the wavelength range of 495 to 570 nm is green (G) light, and light in the wavelength range of 620 to 750 nm is red (R) light.

[0015] The "visible light transmittance" is the A-light source visible light transmittance defined in JIS (Japanese Industrial Standards) R 3212:2015 (Test Methods for Automotive Safety Glass). That is, the transmittance is determined by measuring the transmittance at each wavelength in the wavelength range of 380 to 780 nm using a spectrophotometer with an A-light source, and multiplying the transmittance at each wavelength by a weighting coefficient obtained from the wavelength distribution and wavelength interval of the CIE (Commission Internationale de l'Eclairage) photopic standard relative luminosity factor, and calculating a weighted average. When simply referring to "reflected light" or "transmitted light," this term is used to include scattered light and diffracted light.

[0016] P-polarized light is polarized light that vibrates parallel to the plane of incidence of the light. The plane of incidence is perpendicular to the reflecting surface (such as the surface of a windshield glass) and includes both the incident and reflected light rays. In p-polarized light, the vibration plane of the electric field vector is parallel to the plane of incidence.

[0017] "Projection image" refers to an image based on the projection of light from the projector being used, rather than the surrounding scenery such as the view ahead. A projected image is perceived by an observer as a virtual image that appears to appear beyond the reflective film on the windshield glass. "Screen image" refers to an image displayed on the projector's drawing device or an image drawn by the drawing device on an intermediate image screen or the like. In contrast to a virtual image, a screen is a real image. Both the image and the projected image may be a monochromatic image, a multi-color image with two or more colors, or a full-color image.

[0018] In the present invention, the front retardation Re(λ) and the thickness direction retardation Rth(λ) represent the in-plane retardation and the retardation in the thickness direction (film thickness direction), respectively, at a wavelength λ. Unless otherwise specified, the wavelength λ is 550 nm. In the present invention, Re(λ) and Rth(λ) are values ​​measured at a wavelength λ using an AxoScan OPMF-1 (manufactured by Optoscience). By inputting the average refractive index ((Nx + Ny + Nz) / 3) and film thickness (d (μm)) into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) and Rth(λ) = ((Nx + Ny) / 2 - Nz) × d are calculated.

[0019] In the present invention, the refractive indices Nx, Ny, and Nz are measured using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd.) with a sodium lamp (λ=589 nm) as a light source. Furthermore, when measuring wavelength dependency, measurements can be made using a multi-wavelength Abbe refractometer DR-M2 (manufactured by Atago Co., Ltd.) in combination with an interference filter. Values ​​in the Polymer Handbook (John Wiley & Sons, Inc.) and catalogs for various optical films can also be used. Examples of average refractive index values ​​for major optical films are listed below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), and polystyrene (1.59).

[0020] [Windshield Glass] The windshield glass of the present invention comprises an outer glass plate, a reflective layer composed of a plurality of layers, a retardation layer, an interlayer film, and an inner glass plate, wherein the retardation layer has a front retardation of 280 nm or more and 400 nm or less at a wavelength of 550 nm, and the angle between the direction of the slow axis of the retardation layer and the perpendicular direction to the windshield glass is 1° or more and 20° or less, or 91° or more and 110° or less.

[0021] The term "windshield glass" refers to the window glass and windshield glass of vehicles such as cars and trains, airplanes, ships, motorcycles, and playground equipment. The windshield glass is preferably used as the windshield or windshield glass located in front of the vehicle in the traveling direction.

[0022] An example of a windshield glass is shown in Figure 1. When the windshield glass of the present invention is used in a vehicle, curved glass is often used for the outer glass sheet 1 and the inner glass sheet 2. In this case, if the inner glass sheet 2 faces the inside of the vehicle and the outer glass sheet 1 faces the outside of the vehicle, the convex side of the inner glass sheet 2 is arranged facing the outer glass sheet 1, and the concave side of the outer glass sheet 1 is arranged facing the inner glass sheet 2.

[0023] When the inner glass plate 2 and the outer glass plate 1 are curved glass, in the example shown in Fig. 1 , a retardation layer 6 is disposed on the concave surface side of the inner glass plate 2 via a reflective layer 4 and an adhesive layer 5. That is, in the example shown in Fig. 1 , the reflective layer 4 and the retardation layer 6 are laminated on the surface of the inner glass plate 2 opposite to the outer glass plate 1, and the retardation layer 6 is disposed at a position farther away from the inner glass plate 2 than the reflective layer 4. Therefore, the retardation layer 6 is disposed closer to the vehicle interior than the reflective layer 4.

[0024] Such a windshield glass 10 is used in a head-up display system, in which projection light from a projector is irradiated onto the reflective layer 4 of the windshield glass 10 from inside the vehicle, and a portion of the projection light is reflected by the reflective layer 4 to display an image (virtual image) to the driver. Since the windshield glass 10 is required to have a high visible light transmittance, the reflectance of the reflective layer 4 is at most about 30%, and most of the irradiated projection light passes through the windshield glass 10. In the example shown in FIG. 1 , the projection light is incident on the retardation layer 6 before entering the reflective layer 4.

[0025] Although there is no limitation on the visible light transmittance of the windshield glass, a higher value is preferable. The visible light transmittance of the windshield glass is preferably 70% or more, more preferably more than 70%, even more preferably 75% or more, and particularly preferably 80% or more. The above-mentioned visible light transmittance is preferably satisfied at all positions of the windshield glass, and particularly preferably at the position where the reflective film (reflective layer 4) is present.

[0026] In the windshield glass of the present invention, the reflective layer preferably reflects linearly polarized light. However, the reflective layer does not necessarily have to selectively reflect a specific polarized light. When the reflective layer is incorporated into the windshield glass and used as a combiner for a head-up display, it is preferable that the projected image light be p-polarized light, i.e., linearly polarized light, in order to suppress reflection on the windshield glass surface.

[0027] The shape of the windshield glass is not limited and is determined appropriately depending on the object to which the windshield glass is to be placed. The windshield glass may be, for example, flat or may have a three-dimensional shape with a curved surface such as a concave or convex surface. In a windshield glass shaped for a vehicle to be used, the surface that will be the top side (vertical direction), the observer side, the driver side (horizontal direction), the viewing side such as the inside of the vehicle, and the surface that will be the outside of the vehicle can be specified.

[0028] In the windshield glass 10 of the present invention, the front retardation of the retardation layer 6 at a wavelength of 550 nm is 280 nm or more and 400 nm or less, and the angle between the direction of the slow axis of the retardation layer 6 and the vertical direction of the windshield glass 10 is 1° or more and 20° or 91° or more and 110° or less. In this specification, the vertical direction of the windshield glass 10 refers to the vertical direction (up-down direction) of the windshield glass 10 during normal use, that is, the direction along the surface of the windshield glass 10. Figure 5 shows the vertical direction 31 of the windshield glass 10, the direction 40 of the slow axis of the retardation layer 6, and the angle β they form (slow axis angle).

[0029] As mentioned above, in a head-up display system, it is considered that by introducing p-polarized light into the windshield glass, the reflectance at the air interface of the windshield glass on the vehicle exterior side is reduced, making double images less visible. However, in a head-up display system, light from a projector is reflected by a mirror or the like and enters the windshield glass 10 via a predetermined optical path. Therefore, due to factors such as a misalignment in the mirror position and angle, the linearly polarized light entering the windshield glass 10 may deviate from the ideal p-polarized light and become mixed with an s-polarized component. If an s-polarized component is mixed with the linearly polarized light entering the windshield glass 10, the reflectance of the light that passes through the reflective layer 4 and reaches the air interface of the outer glass plate 1 becomes higher than that of a light containing only p-polarized light. As a result, a portion of the light is reflected, making double images more visible.

[0030] In contrast, the windshield glass 10 of the present invention has a retardation layer 6, and the projected light passes through the retardation layer 6 before reaching the air-interface of the outer glass plate 1. Since the front retardation and slow axis angle of the retardation layer 6 satisfy the above-mentioned ranges, linearly polarized light containing an s-polarized component can be converted into a polarization state closer to p-polarized light. This reduces the reflectance of light that reaches the air-interface of the outer glass plate 1. This suppresses reflection at the air-interface of the outer glass plate 1, thereby reducing double images.

[0031] In the windshield glass 10 of the present invention, the retardation layer 6 having a front retardation and a slow axis angle that satisfy the above ranges can more effectively convert light containing an s-polarized component at a ratio of 10% to 40%, more preferably 12% to 30%, into a state close to p-polarized light, thereby further reducing ghost images.

[0032] In the windshield glass, the reflective layer and the retardation layer may be provided in a projected image display area (projected image reflection area) of the windshield glass. In addition, in the windshield glass, the reflective layer and the retardation layer may be provided between the glass panes of the windshield glass in a laminated glass configuration, or may be provided on the outer surface of the glass pane of the windshield glass.

[0033] When the reflective layer and the retardation layer are provided on the outer surface of the glass plate of the windshield glass, the reflective layer and the retardation layer may be provided inside (on the incident side of the projected image) or outside the vehicle or the like.

[0034] For example, a windshield glass 10b shown in Fig. 6 is an example in which the reflective layer 4 and the retardation layer 6 are disposed on the surface of the inner glass plate 2 opposite to the outer glass plate 1, and the retardation layer 6 is disposed closer to the inner glass plate 2 than the reflective layer 4. Therefore, the retardation layer 6 is disposed closer to the vehicle exterior than the reflective layer 4.

[0035] 7 is an example in which the reflective layer 4 and the retardation layer 6 are disposed between the outer glass plate 1 and the inner glass plate 2, and the retardation layer 6 is disposed closer to the inner glass plate 2 than the reflective layer 4. Therefore, the retardation layer 6 is disposed closer to the vehicle interior than the reflective layer 4.

[0036] 8 is an example in which the reflective layer 4 and the retardation layer 6 are disposed between the outer glass plate 1 and the inner glass plate 2, and the retardation layer 6 is disposed closer to the outer glass plate 1 than the reflective layer 4. Therefore, the retardation layer 6 is disposed closer to the vehicle exterior than the reflective layer 4.

[0037] 7 and 8 , the reflective layer 4, the adhesive layer 5, and the retardation layer 6 are laminated and arranged on the surface of the inner glass plate 2 facing the outer glass plate 1, but this is not limiting and they may also be arranged on the surface of the outer glass plate 1 facing the inner glass plate 2. Alternatively, the reflective layer 4 and the retardation layer 6 may be sandwiched between the outer glass plate 1 and the inner glass plate 2 by the interlayer film 3. Furthermore, one of the reflective layer 4 and the retardation layer 6 may be arranged on the surface of the inner glass plate 2 facing the outer glass plate 1, and the other may be arranged on the surface of the outer glass plate 1 facing the inner glass plate 2. Alternatively, one of the reflective layer 4 and the retardation layer 6 may be arranged between the outer glass plate 1 and the inner glass plate 2, and the other may be arranged on the outer surface of the glass plate.

[0038] When a reflective layer that reflects linearly polarized light (p-polarized light) is used as the reflective layer 4, the retardation layer 6 is preferably disposed closer to the interior of the vehicle than the reflective layer 4 (the configurations shown in FIGS. 1 and 6). As a result, the projected light is incident on the retardation layer 6 before it enters the reflective layer 4, and the projected light is converted by the retardation layer 6 to a state close to p-polarized light before it enters the reflective layer 4. This makes it easier for the light to be reflected by the reflective layer 4 that reflects p-polarized light, thereby increasing the brightness of the displayed image.

[0039] The reflective layer and the retardation layer may be provided on the entire surface of the windshield glass, or may be provided on a portion of the surface of the windshield glass, but are preferably provided on a portion. When the reflective layer and the retardation layer are provided on a portion of the windshield glass, the reflective layer and the retardation layer may be provided at any position on the windshield glass, but are preferably provided so that a virtual image is displayed at a position that is easily visible to an observer such as a driver when used as a HUD. For example, the positions at which the reflective layer and the retardation layer are provided on the windshield glass may be determined based on the relationship between the position of the driver's seat in a vehicle in which the HUD is installed and the position at which the projector is installed.

[0040] The components of the windshield glass of the present invention will be described below.

[0041] <Reflective Layer> The reflective layer is formed of a dielectric layer (dielectric multilayer film) composed of a laminate of inorganic layers with a high refractive index and inorganic layers with a low refractive index, or a linearly polarized light reflective dielectric layer composed of an alternating laminate of optically anisotropic layers and optically isotropic layers. A low reflectance at an incident angle of 0° is preferable for the reflective layer, as this increases the transmittance of the windshield glass. A high reflectance at an incident angle of 65° is preferable, as this increases the visibility of HUD images. Furthermore, it is desirable to control the phase of the reflective layer by adjusting the refractive index and film thickness of each layer, thereby increasing p-polarized light reflection at an incident angle of 65°. Conventionally known configurations can be appropriately used for the dielectric layer composed of a laminate of inorganic layers with a high refractive index and inorganic layers with a low refractive index, and the linearly polarized light reflective layer composed of an alternating laminate of optically anisotropic layers and optically isotropic layers.

[0042] (Inorganic Layer) The high-refractive-index inorganic layer and the low-refractive-index inorganic layer are formed by gas-phase deposition such as magnetron sputtering, and are formed from dielectric layers such as ZnSnMgOx, ZnSnOx, ZnO, SnO2, TiO2, Si3N4, SiO2, MgF2, or AlN. To optimally design the optical properties of the reflective layer, a metal layer such as Ag may be used as a low-refractive-index layer. In the present invention, the dielectric layer may be an alternating layer of high-refractive-index and low-refractive-index layers with a thickness of 1 to 300 nm, and the phase, transmittance, and reflectance can be controlled by adjusting the film thickness and refractive index. In the present invention, it is preferable to configure and deposit the metal layer and the dielectric layer so as to reduce the unpolarized reflectance at an incident angle of 0 degrees and increase the p-polarized reflectance at an incident angle of 65 degrees on the windshield glass.

[0043] (Linearly polarized light reflective dielectric layer) In the linearly polarized light reflective dielectric layer of the present invention, the refractive index n e1 is the refractive index of the isotropic layer n o2 and the refractive index n o1 is the refractive index of the isotropic layer n o2 The multiple optically anisotropic layers are laminated so that their slow axes are parallel to each other. Therefore, as shown in FIG. 2, in one direction (the vertical direction in FIG. 2), the refractive index (n e1 ) and a layer with a high refractive index (no2 On the other hand, in the direction perpendicular to this direction (the left-right direction in FIG. 2), layers with the same refractive index are stacked.

[0044] It is known that a film in which layers with low refractive index (low refractive index layers) and layers with high refractive index (high refractive index layers) are alternately laminated reflects light of a specific wavelength due to structural interference between the many low refractive index layers and the high refractive index layers. Therefore, the linearly polarized light reflective dielectric layer shown in Figure 2 reflects linearly polarized light in the up and down direction in Figure 2 and transmits linearly polarized light in the left and right direction.

[0045] Materials and methods for preparing the linearly polarized light reflective dielectric layer can be those described, for example, in JP-A-9-506837. Specifically, a wide variety of materials can be used to form the reflective layer when processed under conditions selected to achieve a refractive index relationship. Generally, it is necessary for the first material to have a refractive index different from that of the second material in a selected direction. This refractive index difference can be achieved by various methods, including stretching, extrusion, or coating during or after film formation. Furthermore, it is preferable for the two materials to have similar rheological properties (e.g., melt viscosity) so that they can be coextruded.

[0046] Particularly suitable materials for use as linearly polarized light reflective dielectric layers include PEN (polyethylene naphthalate) and PET (polyethylene terephthalate) for optically anisotropic layers, and (isotropically adjusted) PEN, PET, and PMMA (polymethyl methacrylate resin) for isotropic layers.

[0047] <Laminated Glass> The windshield glass may have a laminated glass configuration. The windshield glass of the present invention is a laminated glass and may have the above-mentioned reflective layer between the inner glass sheet and the outer glass sheet. However, a configuration in which a reflective layer is provided on the inner glass sheet is preferred, since this allows for efficient use of reflection at the air interface. Glass sheets commonly used for windshield glass can be used for the inner glass sheet and the outer glass sheet. For example, glass sheets having a visible light transmittance of 80% or less, such as green glass with high heat insulation properties, such as 73% or 76%, may be used. Furthermore, windshield glass is generally rectangular, with its short side in the vertical direction and its long side in the horizontal direction. The laminated glass of the present invention also has its short side in the vertical direction and its long side in the horizontal direction.

[0048] The thickness of the glass plates is not particularly limited, but may be about 0.5 to 5.0 mm, preferably 1.0 to 3.0 mm, and more preferably 2.0 to 2.3 mm. The materials or thicknesses of the inner and outer glass plates may be the same or different.

[0049] A windshield glass having a laminated glass structure can be produced by a known method for producing laminated glass. In general, the windshield glass can be produced by sandwiching an interlayer film for laminated glass between two glass sheets, repeatedly subjecting the interlayer film to heat treatment and pressure treatment (e.g., treatment using a rubber roller) several times, and finally subjecting the interlayer film to heat treatment under pressure using an autoclave or the like.

[0050] (Interlayer Film) The interlayer film prevents glass from penetrating into the interior of the vehicle and scattering in the event of an accident.

[0051] The interlayer film (interlayer film sheet) can be any known interlayer film used as an interlayer film (interlayer layer) in laminated glass. For example, a resin film containing a resin selected from the group consisting of polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, and chlorine-containing resins can be used. The above-mentioned resin is preferably the main component of the interlayer film. Here, the term "main component" refers to a component that accounts for 50% by mass or more of the interlayer film.

[0052] Of the above resins, polyvinyl butyral and ethylene-vinyl acetate copolymer are 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 preferred lower limit of the degree of acetalization of the above polyvinyl butyral is 40%, and the preferred upper limit is 85%, with a more preferred lower limit being 60% and a more preferred upper limit being 75%.

[0053] 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. The preferred lower limit of the polymerization degree of the polyvinyl alcohol is 200, and the preferred upper limit is 3000. When the polymerization degree of polyvinyl alcohol is 200 or more, the penetration resistance of the resulting laminated glass is less likely to decrease, and when it is 3000 or less, the resin film has good formability and does not become too rigid, resulting in good processability. The more preferred lower limit is 500, and the more preferred upper limit is 2000.

[0054] There is also no limitation on the thickness of the interlayer, and the thickness may be set according to the forming material, etc., in the same way as the interlayer of known windshield glass.

[0055] <Retardation layer> The retardation layer is not particularly limited as long as the front retardation is 280 nm to 400 nm, and can be appropriately selected according to the purpose. Examples of the retardation layer include a stretched polycarbonate film, a stretched norbornene-based polymer film, a transparent film containing and oriented inorganic particles having birefringence such as strontium carbonate, a thin film obtained by obliquely depositing an inorganic dielectric on a support, a film in which a polymerizable liquid crystal compound is uniaxially oriented and fixed in orientation, and a film in which a liquid crystal compound is uniaxially oriented and fixed in orientation.

[0056] Among them, a film in which a polymerizable liquid crystal compound is uniaxially aligned and fixed is a suitable example of a retardation layer. For example, such a retardation layer can be formed by applying a liquid crystal composition containing a polymerizable liquid crystal compound to a temporary support or the surface of an alignment layer, forming the polymerizable liquid crystal compound in the liquid crystal composition into a nematic alignment in a liquid crystal state, and then fixing the alignment by curing.

[0057] The retardation layer may be a layer obtained by applying a composition containing a polymer liquid crystal compound to the surface of a temporary support or an alignment layer, etc., to form a nematic alignment in a liquid crystal state, and then cooling to fix the alignment.

[0058] The thickness of the retardation layer is not particularly limited, but is preferably 0.2 μm to 300 μm, more preferably 0.5 μm to 150 μm, and even more preferably 1.0 μm to 80 μm. The thickness of the retardation layer formed from the liquid crystal composition is not particularly limited, but is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 5.0 μm, and even more preferably 0.7 μm to 3.0 μm.

[0059] The retardation layer preferably has a front retardation of 280 nm to 400 nm at a wavelength of 550 nm, more preferably 320 nm to 350 nm. By setting the front retardation of the retardation layer within this range, it is possible to more effectively suppress ghost images. In this case, Rth is preferably about 140 nm to 200 nm.

[0060] The retardation layer is disposed so that the projected light from the projector becomes p-polarized light at the air interface of the outer glass plate, and the angle β between the slow axis direction of the retardation layer and the vertical direction of the windshield glass is appropriately set. The angle β is preferably 1° to 20° or 91° to 110°, and more preferably 2° to 10° or 92° to 100°. By setting the angle β in this range, double images can be more effectively suppressed.

[0061] [Head-up display system] Next, a head-up display (HUD) having the windshield glass of the present invention will be described. The head-up display system of the present invention has the above-mentioned windshield glass and a projector that irradiates projection light onto the first glass plate side of the windshield glass.

[0062] Fig. 3 shows an example of a head-up display system (HUD) according to the present invention. The HUD 20 shown in Fig. 3 includes a windshield glass 10 and a projector 7. The HUD 20 is used in a vehicle such as a passenger car.

[0063] In the HUD 20, the projector 7 ideally projects p-polarized light onto the windshield glass 10, but may also project light containing both p- and s-polarized components. In the following description, non-ideal light containing both p- and s-polarized components is also referred to as p-polarized light. If the light projected by the projector 7 onto the windshield glass 10 is ideally p-polarized, reflection of the projected light by the outer glass plate 1 and inner glass plate 2 of the windshield glass 10 can be significantly reduced, thereby preventing problems such as double images. Preferably, the projector 7 projects p-polarized light onto the windshield glass at the Brewster angle. This eliminates reflection of the projected light by the outer glass plate 1 and inner glass plate 2, enabling a clearer image to be displayed.

[0064] In the HUD 20 of the present invention, the polarization of the projected light is determined by the direction of the transmission axis of the polarizer when the projected light appears brightest when transmitted through the polarizer. As shown in Figure 4, the polarization of the projected light 30 is a vector, with the direction 31 perpendicular to the windshield glass being the p-polarized component and the direction 32 parallel to the windshield glass being the s-polarized component. The proportion of the s-polarized component is calculated as s-polarized component / (s-polarized component + p-polarized component) × 100%. The projector 7 emits projection light that is primarily p-polarized, but due to factors such as the mirror arrangement within the projector, the s-polarized component is mixed in the emitted light, resulting in a proportion of the s-polarized component of 10% or more. This makes it easier to observe double images compared to when the projected light is ideally p-polarized only.

[0065] In contrast, as described above, the windshield glass of the present invention has a retardation layer whose front retardation and slow axis angle satisfy the above-mentioned ranges, so that linearly polarized light mixed with an s-polarized component can be converted into a polarization state closer to ideal p-polarized light. This makes it possible to suppress reflection at the air interface of the outer glass plate 1 and reduce ghost images. The present invention is preferably applied when the ratio of the s-polarized component is 10% to 40%, and more preferably when it is 12% to 30%.

[0066] <Projector> A "projector" is a "device that projects light or an image," and includes a "device that projects a drawn image," emitting projection light that carries the image to be displayed. In the HUD of the present invention, the projector preferably emits p-polarized projection light. In the HUD, the projector is only required to be positioned so that the p-polarized projection light that carries the image to be displayed can be incident on the reflective film in the windshield glass at an oblique angle of incidence.

[0067] In a HUD, the projector preferably includes a drawing device and reflects and displays an image (real image) drawn on a small intermediate image screen as a virtual image using a combiner. Any known projector used in HUDs can be used as the projector as long as it can emit p-polarized projection light. Furthermore, it is preferable that the projector be one in which the imaging distance of the virtual image, i.e., the imaging position of the virtual image, is variable.

[0068] Examples of methods for changing the imaging distance of a virtual image in a projector include a method of moving the image generation surface (screen) (see JP 2017-21302 A), a method of switching between multiple optical paths with different optical path lengths (see WO 2015 / 190157 A), a method of changing the optical path length by inserting and / or moving a mirror, a method of changing the focal length by using a lens assembly as an imaging lens, a method of moving the projector, a method of switching between multiple projectors with different virtual image imaging distances, and a method of using a variable focus lens (see WO 2010 / 116912 A).

[0069] The projector may be one that can continuously change the virtual image formation distance, or one that can switch the virtual image formation distance at two or more points. It is preferable that at least two of the virtual images projected by the projector have different formation distances of 1 meter or more. Therefore, if the projector is one that can continuously change the virtual image formation distance, it is preferable that the virtual image formation distance can be changed by 1 meter or more. Using such a projector is preferable because it can be used effectively even when the driver's line of sight distance differs significantly, such as when driving at normal speeds on an ordinary road and when driving at high speeds on an expressway.

[0070] (Drawing device) A drawing device may be a device that displays an image by itself, or may be a device that emits light capable of drawing an image. In a drawing device, light from a light source may be adjusted by a drawing method such as a light modulator, a laser intensity modulation means, or a light deflection means for drawing. A drawing device refers to a device that includes a light source and further includes a light modulator, a laser intensity modulation means, or a light deflection means for drawing, etc., depending on the drawing method.

[0071] (Light Source) There are no limitations on the light source, and known light sources used in projectors, drawing devices, displays, etc., 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.

[0072] (Drawing Method) The drawing method can be selected according to the light source to be used, etc., and is not particularly limited. Examples of drawing methods include a fluorescent display tube, an LCD (Liquid Crystal Display) method using liquid crystal, an LCOS (Liquid Crystal on Silicon) method using liquid crystal, a DLP (registered trademark) method (Digital Light Processing), and a scanning method using a laser. The drawing method may be a method using a fluorescent display tube integrated with a light source. The LCD method is preferred as the drawing method.

[0073] In the LCD and LCOS systems, the light of each color is modulated and combined by an optical modulator and emitted from a projection lens.The DLP system is a display system that uses a DMD (Digital Micromirror Device), and an image is drawn using micromirrors arranged in the same number as the pixels, and the light is emitted from a projection lens.

[0074] The scanning method involves scanning a light beam across a screen and utilizing the afterimage of the eye to create a contrast image. For example, see JP-A-7-270711 and JP-A-2013-228674. In a laser scanning method, intensity-modulated laser beams of, for example, red, green, and blue light are combined into a single beam using a multiplexing optical system or a condenser lens, and the beam is scanned by an optical deflection device to form an image on an intermediate image screen (described below). In the scanning method, for example, the intensity modulation of the red, green, and blue laser beams may be performed directly by changing the intensity of the light source or by using an external modulator. Examples of optical deflection devices include a galvanometer mirror, a combination of a galvanometer mirror and a polygon mirror, and a MEMS (Micro Electro Mechanical Systems), among which MEMS is preferred. Examples of scanning methods include a random scan method and a raster scan method, with the raster scan method being preferred. In the raster scan method, the laser light can be driven, for example, at a resonant frequency in the horizontal direction and a sawtooth wave in the vertical direction. Since the scanning method does not require a projection lens, it is easy to make the device smaller.

[0075] The light emitted from the imaging device may be linearly polarized or natural light (unpolarized). Imaging devices using LCD or LCOS imaging methods and imaging devices using laser light sources essentially emit linearly polarized light. In imaging devices that emit linearly polarized light and contain light of multiple wavelengths (colors), it is preferable that the polarization directions (transmission axis directions) of the light of the multiple wavelengths are the same. It is known that some commercially available imaging devices emit light with non-uniform polarization directions in the red, green, and blue wavelength regions (see JP 2000-221449 A). Specifically, there is known an example in which the polarization direction of green light is perpendicular to the polarization directions of red light and blue light. As described above, in the HUD of the present invention, the projection light emitted by the projector is preferably p-polarized.

[0076] (Intermediate Image Screen) As described above, the rendering device may use an intermediate image screen. An "intermediate image screen" is a screen on which an image is rendered. That is, when light emitted from the rendering device is not yet visible as an image, the rendering device forms a visible image on the intermediate image screen using this light. The image rendered on the intermediate image screen may be projected onto the combiner by light passing through the intermediate image screen, or may be projected onto the combiner by light reflected from the intermediate image screen.

[0077] Examples of intermediate image screens include scattering films, microlens arrays, and rear-projection screens. 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 polarized light incident on the intermediate image screen are disturbed, making the combiner (reflective layer) prone to color unevenness. However, using a retardation film with a predetermined phase difference can reduce this color unevenness problem. An intermediate image screen that has the function of widening and transmitting incident light is preferred, as this enables the projected image to be displayed in an enlarged scale. Examples of such intermediate image screens include screens composed of microlens arrays. Microarray lenses used in HUDs are described, for example, in Japanese Patent Application Laid-Open Nos. 2012-226303, 2010-145745, and 2007-523369. The projector may also include a reflector or the like that adjusts the optical path of the projected light formed by the imaging device.

[0078] For HUDs using windshield glass having a reflective layer, reference can be made to Japanese Patent Application Laid-Open Nos. 2-141720, 10-96874, 2003-98470, U.S. Pat. No. 5,013,134, and Japanese Patent Publication No. 2006-512622.

[0079] The windshield glass is particularly useful for HUDs that are used in combination with projectors that use lasers, LEDs, OLEDs (organic light-emitting diodes), etc., whose light emission wavelengths are not continuous in the visible light range, as light sources. It can also be used for projecting displays that emit polarized light, such as LCDs (liquid crystal displays).

[0080] [Projected Light (Incident Light)] Incident light is preferably incident at an oblique angle of 45° to 70° relative to the normal to the reflective layer. The Brewster angle at the interface between glass with a refractive index of approximately 1.51 and air with a refractive index of 1 is approximately 56°. By making p-polarized light incident within this angle range, the amount of incident light for projected image display reflected by the surface of the windshield glass on the viewing side can be reduced, enabling image display with minimal double images. It is also preferable that the angle be 50° to 65°. In this case, it is sufficient that the projected image can be observed on the side of incidence of the projection light, on the opposite side of the incident light, at an angle of 45° to 70°, preferably 50° to 65°, relative to the normal to the selective reflection layer.

[0081] The incident light may be incident from any direction, such as above, below, left, or right, depending on the viewing direction. For example, it is preferable that the incident light be incident from below at an oblique angle as described above when in use. Furthermore, it is preferable that the reflective layer of the windshield glass is arranged to reflect incident p-polarized light.

[0082] As described above, the projected light used to display a projected image in the HUD of the present invention is preferably p-polarized light, vibrating in a direction parallel to the plane of incidence. If the light emitted from the projector is not linearly polarized, it may be converted to p-polarized light by providing a linear polarizing film (polarizer) on the projector's output side, or by a known method using a linear polarizing film or the like in the optical path from the projector to the windshield glass. In this case, the component that converts non-linearly polarized projected light to p-polarized light is also considered to constitute the projector in the HUD of the present invention. As described above, for projectors whose output light does not have a uniform polarization direction across the red, green, and blue wavelength ranges, it is preferable to wavelength-selectively adjust the polarization direction so that all color wavelength ranges are p-polarized.

[0083] In the HUD 20 of the present invention, the projector 7 emits projection light that is primarily p-polarized light, but as mentioned above, due to the influence of the mirror arrangement inside the projector, etc., s-polarized light components are mixed in with the emitted light, and the ratio of s-polarized light components is 10% or more.

[0084] As described above, the HUD (projector) may be a projection system that allows a virtual image to be formed at a variable position. By allowing the virtual image to be formed at a variable position, the driver can view the virtual image more comfortably and conveniently. The virtual image is formed at a position where the virtual image can be viewed by the driver of the vehicle, and is typically, for example, at a position beyond the windshield glass, 1000 mm or more away from the driver.

[0085] The present invention is basically configured as described above. While the windshield glass and head-up display system (HUD) of the present invention have been described in detail above, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the spirit and scope of the present invention.

[0086] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following examples.

[0087] [Example 1] <Preparation of Windshield Glass> A windshield glass was prepared by preparing a laminated glass using an outer glass sheet, an interlayer film, and an inner glass sheet as described below, and then attaching a linearly polarized reflective film (reflective layer) and a retardation film (retardation layer) prepared as described below with an adhesive.

[0088] (Preparation of Laminated Glass) As the outer and inner glass plates, float glass (FL2, manufactured by Central Glass Co., Ltd., visible light transmittance 90%) having a height of 200 mm and a thickness of 2 mm was used. A 0.76 mm thick PVB film (interlayer, manufactured by Sekisui Chemical Co., Ltd.) was sandwiched between the outer and inner glass plates, and the laminate was held at 90°C and 10 kPa (0.1 atmosphere) for one hour, and then heated in an autoclave (manufactured by Kurihara Manufacturing Co., Ltd.) at 115°C and 1.3 MPa (13 atmosphere) for 20 minutes to remove bubbles, thereby preparing laminated glass.

[0089] <Preparation of Linearly Polarized Reflective Film> Based on the method described in JP-A-9-506837, a linearly polarized reflective film (linearly polarized reflective layer) was prepared as follows.

[0090] 2,6-Polyethylene naphthalate (PEN) and a 70% naphthalate / 30% terephthalate copolyester (coPEN) were each synthesized in a standard polyester resin synthesis reactor using ethylene glycol as the diol. Monolayer films of PEN and coPEN were extruded, stretched at approximately 150°C with a 5:1 draw ratio, and heat-treated at approximately 230°C for 30 seconds. The refractive index of the PEN film along its slow axis (orientation axis) was approximately 1.86, that of the transverse axis was 1.64, and that of the coPEN film was approximately 1.64.

[0091] By adjusting the stretch ratio, the refractive index of the PEN film along the slow axis was found to be about 1.71, that along the transverse axis was found to be 1.64, and that of the coPEN film was found to be about 1.64. That is, the difference Δn between the refractive index of the optically anisotropic layer along the slow axis and that of the isotropic layer was found to be 0.07.

[0092] Next, PEN and coPEN were coextruded using a 25-slot feed block equipped with a standard extrusion die to form 16 alternating layers of PEN and coPEN with the thicknesses shown in (1) of Table 1. The same procedure was repeated to form 16 alternating layers of PEN and coPEN in order with the thicknesses shown in (2) to (6) of Table 1, thereby producing a laminate having a total of 96 layers.

[0093]

[0094] Next, the stretched laminate was heat-treated in an air oven at about 230°C for 30 seconds to produce a linearly polarized reflective film. The produced linearly polarized reflective film had a thickness of about 10 µm. The reflection spectrum of this linearly polarized reflective film was measured using a spectrophotometer (manufactured by JASCO Corporation, V-670). Reflectance peaks were observed in the reflection bands of 450 nm, 550 nm, 650 nm, 700 nm, 750 nm, and 800 nm, and a reflection spectrum with a p-polarized light reflectance of 28% was obtained at an incident angle of 65°.

[0095] <Preparation of Retardation Layer> (Preparation of Coating Solution for Forming Retardation Layer) The following components were mixed to prepare a coating solution for forming a retardation layer having the following composition.

[0096] ------------------------------------------------------------------ Coating liquid for forming retardation layer ------------------------------------------------------------------ Mixture 1: 100 parts by mass Fluorine-based horizontal alignment agent 1 (alignment control agent 1): 0.05 parts by mass Fluorine-based horizontal alignment agent 2 (alignment control agent 2): 0.01 parts by mass Polymerization initiator IRGACURE OXE01 (manufactured by BASF): 1.0 part by mass Solvent (methyl ethyl ketone): Amount to make the solute concentration 20% by mass

[0097]

[0098]

[0099]

[0100] A cellulose acylate film (thickness: 40 μm) was used as a support, and the following alignment film was formed on the support, and then a retardation layer was formed.

[0101] (Formation of Alignment Film) A coating liquid for forming an alignment film having the composition shown below was applied onto a support at a rate of 24 mL / m using a wire bar coater. 2 The coating was then dried with hot air at 100°C for 120 seconds.

[0102] ------------------------------------------------------------------ Composition of coating liquid for forming alignment film -------------------------------------------------- Modified polyvinyl alcohol shown below: 28 parts by mass Citrate ester (AS3, manufactured by Sankyo Chemical Co., Ltd.) 1.2 parts by mass Photoinitiator (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 ------------------------------------------------------------------

[0103] (Modified polyvinyl alcohol)

[0104]

[0105] The formed coating film was subjected to a rubbing treatment (rayon cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm (revolutions per minute), conveying speed: 10 m / min, number of strokes: 1 round trip) in a direction rotated 6° clockwise from the long side direction of the support as a reference, to form an alignment film.

[0106] The retardation layer forming coating solution was applied to the surface of the alignment film on the support using a wire bar, and then dried. Then, the substrate was placed on a hot plate at 50°C, and heated with an electrodeless lamp "D bulb" (60 mW / cm) manufactured by Fusion UV Systems in an environment with an oxygen concentration of 1000 ppm or less. 2) for 6 seconds to fix the liquid crystal phase. This resulted in a retardation layer having a desired front retardation, i.e., a thickness adjusted to obtain a desired front retardation. The front retardation of the prepared retardation layer was measured with an AxoScan and found to be 330 nm.

[0107] Next, a linearly polarized reflective film and a retardation layer were adhered in this order to the prepared laminated glass using an OCA (MHM-UVC15, manufactured by Nichiei Kako Co., Ltd.). The linearly polarized reflective film was adhered so that the vertical direction (up-down direction) of the laminated glass coincided with the direction of the reflection axis (slow axis of the optically anisotropic layer). The retardation layer was adhered so that the direction rotated 6° from the vertical direction (up-down direction) of the laminated glass coincided with the rubbing direction of the alignment film, i.e., the slow axis. The vertical direction of the laminated glass here refers to the short side direction of the glass (200 mm side). In this way, a windshield glass having a layer structure of outer glass plate / intermediate layer / inner glass plate / OCA / linearly polarized reflective layer / OCA / retardation layer / cellulose acylate film was prepared. (Example 1)

[0108] [Example 2] After preparing a laminated glass in the same manner as in Example 1, a reflective layer made of an inorganic dielectric layer was formed by magnetron sputtering on the surface of the inner glass sheet opposite to the outer glass sheet. ３ N ４ and the low refractive index layer is SiO ２ , as the metal layer Ag, from the inner glass plate side, inner glass plate / Si ３ N ４ 12 nm / SiO ２ 179 nm / Si ３ N ４ 54nm / Ag 14nm / Si ３ N ４ 18 nm / SiO ２ It was formed in a 49 nm configuration.

[0109] The reflection spectrum of this inorganic dielectric layer was measured with a spectrophotometer (V-670, manufactured by JASCO Corporation), and the reflection spectrum showed a p-polarized light reflectance of 27% at an incident angle of 65°.

[0110] Next, a retardation layer was prepared in the same manner as in Example 1, and then the retardation layer was attached to the inorganic dielectric layer of the prepared inorganic dielectric layer laminated glass using an OCA (MHM-UVC15, manufactured by Nichiei Kako Co., Ltd.). The retardation layer was attached so that the direction rotated 6° from the vertical direction (up-down direction) of the laminated glass coincided with the rubbing direction of the alignment film, i.e., the direction of the slow axis. In this way, a windshield glass having a layer structure of outer glass plate / intermediate layer / inner glass plate / inorganic dielectric layer / OCA / retardation layer / cellulose acylate film was prepared. (Example 2)

[0111] [Examples 3 to 17 and Comparative Examples 1 to 8] Windshield glasses of Examples 3 to 17 and Comparative Examples 1 to 8 were produced in the same manner as in Example 1 or Example 2, except that the layer structure, the presence or absence of a retardation layer, the type of reflective layer, the Re and Rth of the retardation layer, and the angle of the retardation layer were changed as shown in Table 2. The structures of each Example and Comparative Example are shown in Table 2. The retardation layers of Examples 4, 14 to 15, and Comparative Examples 7 to 8 were produced in the same manner as the retardation layer of Example 1, except that the thicknesses were adjusted to achieve the Re and Rth shown in Table 2.

[0112] In Example 16, before preparing the laminated glass, a linearly polarized reflective film and a retardation layer were prepared in the same manner as in Example 1, and the linearly polarized reflective film and the retardation layer were sequentially attached to the inner surface of the outer glass plate (the surface facing the inner glass plate) using OCA (MHM-UVC15, manufactured by Nichiei Kako Co., Ltd.). Then, a PVB film and an inner glass plate were superimposed on the surface of the outer glass plate to which the linearly polarized reflective film and the retardation layer were attached, and laminated glass was prepared in the same manner as in Example 1. The linearly polarized reflective film was attached so that the vertical direction (up-down direction) of the laminated glass and the direction of the reflection axis coincided. The retardation layer was attached so that the direction rotated 6° relative to the vertical direction (up-down direction) of the laminated glass coincided with the rubbing direction of the alignment film, i.e., the slow axis. That is, in Example 16, a windshield glass having a layer structure of outer glass plate / OCA / linearly polarized light reflective layer / OCA / retardation layer / cellulose acylate film / intermediate layer / inner glass plate was produced.

[0113] In Example 17, before preparing the laminated glass, a reflective layer made of an inorganic dielectric layer was formed on the inner surface of the outer glass plate (the surface facing the inner glass plate) in the same manner as in Example 2, and a retardation layer was attached to the inorganic dielectric layer using OCA (MHM-UVC15, manufactured by Nichiei Kako Co., Ltd.). A PVB film and an inner glass plate were then superimposed on the surface of the outer glass plate on which the inorganic dielectric layer and retardation layer had been attached, thereby preparing the laminated glass in the same manner as in Example 1. The inorganic dielectric layer was formed so that the vertical direction (up-down direction) of the laminated glass coincided with the direction of the reflection axis. The retardation layer was attached so that the direction rotated 6° relative to the vertical direction (up-down direction) of the laminated glass coincided with the rubbing direction of the alignment film, i.e., the slow axis. That is, in Example 17, a windshield glass was prepared having a layer structure of outer glass plate / inorganic dielectric layer / OCA / retardation layer / cellulose acylate film / interlayer / inner glass plate.

[0114]

[0115] [Brightness Evaluation] <Evaluation of p-polarized reflectance> Linearly polarized light having a p-polarized component ratio of 80% and an s-polarized component ratio of 20% was incident from the inner glass plate side in a direction at an angle of 65° relative to the normal direction of the inner glass plate, and the reflectance spectrum of the specularly reflected light (in the direction opposite to the normal direction within the incident plane, at an angle of 65° relative to the normal direction) was measured using a spectrophotometer (V-670, manufactured by JASCO Corporation). The s-polarized component ratio was determined as shown in FIG. 4 , with the polarized light 30 of the projected light as a vector, the p-polarized component in the direction perpendicular to the windshield glass 31 (the direction of the short side 200 mm), and the s-polarized component in the direction parallel to the windshield glass 32 (the direction of the long side 300 mm). The s-polarized component ratio was calculated as s-polarized component / (s-polarized component + p-polarized component) × 100%. In accordance with JIS R3106, the reflectance of the projected image was calculated by multiplying the reflectance by a coefficient corresponding to the visual sensitivity and the emission spectrum of the D65 light source at wavelengths of 380 to 780 nm in 10 nm increments, and the calculated reflectance was evaluated as brightness. The brightness was evaluated according to the following evaluation criteria.

[0116] <Evaluation of Image Visibility> The windshield glass was installed as the front glass of a vehicle, and an image was projected from a projector with a daytime road as the background, and the HUD display image was observed. The HUD display image displayed characters in white, green, and red. The visibility of the displayed image was evaluated according to the following evaluation criteria. Note that the brightness rating is higher when the reflection at a wavelength around 555 nm is strong, so when the brightness rating is low, the visibility of red is more likely to decrease than that of green and white.

[0117] Evaluation criteria for brightness (p-polarized reflectance) and image visibility A: 26% or more White, green, and red letters could be read. B: 20% or more but less than 26% White and green letters were visible, and red letters were just barely readable. C: Less than 20% White and green letters were visible, but red letters were faint and unreadable.

[0118] [Evaluation of double images] As in the evaluation of p-polarized reflectance described above, linearly polarized light with an s-polarized component ratio of 20% was incident on the windshield glass at an incident angle of 65°, and double images were visually confirmed using an image of a white line grid drawn on a black background. Evaluation criteria for double images: A: No double images of the white lines were visible. B: The double images of the white lines were very faint (a level that is not problematic in practical use). C: The double images of the white lines were visible. The results are shown in Table 3.

[0119]

[0120] As shown in Table 3, it can be seen that the examples of the present invention provide better results in terms of double images than the comparative examples.

[0121] Furthermore, comparison of Examples 1 to 9 and 14 to 15 with Comparative Examples 3 and 4, and comparison of Examples 10 to 13 with Comparative Examples 5 and 6 reveals that the angle of the slow axis of the retardation layer may be 1° or more and 20° or less, or 91° or more and 110° or less.

[0122] Furthermore, by comparing Example 1 with Examples 2 and 5, it can be seen that when the reflective layer is a linearly polarized light reflective layer, the brightness of the displayed image is higher when the retardation layer is located closer to the inside of the vehicle than the reflective layer.

[0123] Furthermore, a comparison of Examples 1, 3, and 6 to 9 reveals that the angle of the slow axis of the retardation layer is preferably 2° or more and 10° or less, and a comparison of Examples 10 to 13 reveals that the angle of the slow axis of the retardation layer is also preferably 92° or more and 100° or less.

[0124] Furthermore, a comparison of Examples 2, 4, and 14 to 15 reveals that the front retardation of the retardation layer at a wavelength of 550 nm is preferably 320 nm or more and 350 nm or less.

[0125] Furthermore, Examples 16 and 17 show that the structure in which the reflective layer and the retardation layer are disposed between the outer glass plate and the inner glass plate also provides the same effects as the structure in which the reflective layer and the retardation layer are disposed on the outer surface of the laminated glass. From the above results, the effects of the present invention are clear.

[0126] The present invention can be suitably used in an in-vehicle head-up display system (HUD), etc.

[0127] DESCRIPTION OF SYMBOLS 1 outer glass plate 2 inner glass plate 3 intermediate film 4 reflective layer 5 adhesive layer 6 retardation layer 7 projector 8 driver 9 incident angle 10, 10b to 10d windshield glass 20 head-up display system (HUD) 30 polarization direction of incident light 31 vertical direction of windshield glass 32 horizontal direction of windshield glass 40 direction of slow axis of retardation layer

Claims

1. A windshield glass comprising an outer glass plate, a reflective layer consisting of multiple layers, a retardation layer, an intermediate layer and an inner glass plate, wherein the front retardation of the retardation layer at a wavelength of 550 nm is 280 nm or more and 400 nm or less, and the angle between the direction of the slow axis of the retardation layer and the vertical direction of the windshield glass is 1° or more and 20° or less, or 91° or more and 110° or less.

2. The windshield glass according to claim 1, wherein the front retardation of the phase difference layer at a wavelength of 550 nm is 320 nm or more and 350 nm or less.

3. The windshield glass according to claim 1, wherein the angle between the direction of the slow axis of said retardation layer and the perpendicular direction of said windshield glass is from 2° to 10°, or from 92° to 100°.

4. A windshield glass according to claim 1, wherein the reflective layer and the retardation layer are disposed between the outer glass plate and the inner glass plate, and the retardation layer is disposed closer to the inner glass plate than the reflective layer.

5. A windshield glass according to claim 1, wherein the reflective layer and the retardation layer are disposed between the outer glass plate and the inner glass plate, and the retardation layer is disposed closer to the outer glass plate than the reflective layer.

6. A windshield glass according to claim 1, wherein the reflective layer and the retardation layer are disposed on a surface of the inner glass plate opposite to the outer glass plate, and the retardation layer is disposed at a position farther away from the inner glass plate than the reflective layer.

7. A windshield glass according to claim 1, wherein the reflective layer and the retardation layer are disposed on a surface of the inner glass plate opposite the outer glass plate, and the retardation layer is disposed closer to the inner glass plate than the reflective layer.

8. The windshield glass according to claim 1, wherein the reflective layer is a reflective layer in which an inorganic layer is laminated.

9. The windshield glass according to claim 1, wherein the reflective layer is a linearly polarized light reflective layer made of an optically anisotropic layer and an optically isotropic layer laminated alternately.

10. A head-up display system comprising the windshield glass according to any one of claims 1 to 9 and a projector that irradiates projection light onto the inner glass plate side of the windshield glass.

11. The head-up display system according to claim 10, wherein the light projected by the projector contains an s-polarized component and a p-polarized component, and the ratio of the s-polarized component is 10% or more and 40% or less.