Linear polarized light reflective film, windshield and head-up display system

Abstract

Provided are a linearly polarized light reflective film, a windshield, and a head-up display system that have high visible light transmittance and are capable of improving the brightness and color of displayed images. The linearly polarized light reflective film comprises a selective reflective layer formed by laminating an optically anisotropic layer and an isotropic layer, wherein the selective reflective layer satisfies any of the following conditions: having at least one first reflective peak with a central reflection wavelength of 430 nm to less than 500 nm and a reflectivity of 10% to 20%; having at least one second reflective peak with a central reflection wavelength of 530 nm to less than 600 nm and a reflectivity of 10% to 20%; having a third reflective peak with a central reflection wavelength of 600 nm to 800 nm, wherein the third reflective peak has two or more reflective peaks and a reflectivity of 10% to 20% or less, or having a single reflective peak, a reflectivity of 10% to 20% and a wavelength bandwidth of 120 nm or more.

Description

Technical Field

[0001] The present invention relates to a linearly polarized light reflecting film that can be used as a combiner of a head-up display system, a windshield having the linearly polarized light reflecting film, and a head-up display system. Background Art

[0002] Currently, there is known a technology called a head-up display or head-up display system, which projects an image onto the windshield of a vehicle or the like and provides the driver or the like with various information such as a map, driving speed, and vehicle status.

[0003] In a head-up display system, a virtual image projected onto the windshield, including the various aforementioned information, is visible to the driver and others. The virtual image is positioned forward of the windshield, toward the vehicle's exterior. This virtual image is typically positioned at least 1000 mm forward of the windshield, toward the exterior. This allows the driver to obtain the aforementioned information while observing the exterior world ahead, without having to significantly shift their line of sight. Therefore, when using a head-up display system, the expectation is that the driver can obtain various information while driving more safely.

[0004] A head-up display system can be constructed by forming a linearly polarized light reflecting film on a windshield using a half mirror film. Various half mirror films that can be used for a head-up display system have been proposed.

[0005] Patent Document 1 describes a light-reflecting film comprising one or more light-reflecting layers: a light-reflecting layer PRL-1 having a central reflection wavelength of 400 nm to less than 500 nm and a reflectivity of 5% to 25% with respect to ordinary light at the central reflection wavelength; a light-reflecting layer PRL-2 having a central reflection wavelength of 500 nm to less than 600 nm and a reflectivity of 5% to 25% with respect to ordinary light at the central reflection wavelength; and a light-reflecting layer PRL-3 having a central reflection wavelength of 600 nm to less than 700 nm and a reflectivity of 5% to 25% with respect to ordinary light at the central reflection wavelength. The at least two or more light-reflecting layers having different central reflection wavelengths are stacked, and the at least two or more stacked light-reflecting layers each reflect light polarized in the same direction.

[0006] The light reflective film described in Patent Document 1 is incorporated into a windshield, for example, to form a head-up display system. In addition to high visible light transmittance, the windshield (combiner) forming the head-up display system is required to allow the driver to visually recognize images even when wearing polarized sunglasses.

[0007] Light reflected from things like the hood of an oncoming vehicle or from water on the road, which can be obstacles while driving, is primarily s-polarized light. Polarized sunglasses, on the other hand, block s-polarized light. Therefore, wearing polarized sunglasses prevents you from being glared by light reflected from oncoming vehicles' hoods or from water on the road, which can be obstacles while driving.

[0008] The light reflective film described in Patent Document 1 is a half mirror that reflects p-polarized light in order to display a projected image using p-polarized light. Therefore, even when wearing polarized sunglasses that cut off s-polarized light, the image of the head-up display system can be visually recognized.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: International Publication No. 2016 / 056617 Summary of the Invention

[0012] Technical issues to be solved by the invention

[0013] Here, in-vehicle head-up display systems are required to have a transparent appearance even when viewed from various angles, from the perspectives of transmittance exceeding legal requirements and design quality.

[0014] In order to maintain the legally required transmittance of 70% or more and make the appearance color close to transparent, reducing the reflectivity has been considered. However, if the reflectivity is reduced too much, the brightness of the displayed image (projected image) will decrease, and the visibility will be reduced.

[0015] The present invention aims to provide a linearly polarized light reflective film having high visible light transmittance, which can improve the brightness of a displayed image and good transparency of the appearance color, and a windshield and a head-up display system using the linearly polarized light reflective film.

[0016] Means for solving technical problems

[0017] [1] A linearly polarized light reflecting film comprising a selective reflecting layer formed by laminating an optically anisotropic layer and an isotropic layer,

[0018] Select a reflective layer that meets all of the following conditions:

[0019] (i) having at least one first reflection peak with a central reflection wavelength of 430 nm or more and less than 500 nm, and a natural light reflectivity of 10% or more and 20% or less in the first reflection peak

[0020] (ii) having at least one second reflection peak with a central reflection wavelength of 530 nm or more and less than 600 nm, and a natural light reflectivity in the second reflection peak of 10% or more and 20% or less

[0021] (iii) having a third reflection peak with a central reflection wavelength of 600 nm to 800 nm, and the third reflection peak satisfies any of the following conditions:

[0022] (a) It has two or more reflection peaks, and the natural light reflectivity is 10% or more and 20% or less.

[0023] (b) There is one reflection peak, the natural light reflectance is 10% to 20%, and the wavelength bandwidth of the region where the reflectance is higher than the average of the maximum and minimum reflectances at 600 nm to 800 nm is 120 nm or more.

[0024] [2] The linearly polarized light reflective film according to [1], wherein

[0025] The intensity ratio of the first reflection peak to the second reflection peak is 80% or more and 120% or less.

[0026] The intensity ratio of the first reflection peak to the third reflection peak is 80% or more and 120% or less.

[0027] The intensity ratio of the second reflection peak to the third reflection peak is 80% or more and 120% or less.

[0028] [3] The linearly polarized light reflective film according to [1] or [2], wherein

[0029] The wavelength bandwidth of the region where the reflectivity is higher than the average of the maximum and minimum values of the reflectivity of the first reflection peak at 430 nm to 500 nm is 20 nm to 95 nm.

[0030] The wavelength bandwidth of the region where the reflectance is higher than the average value of the maximum and minimum values of the reflectance at the second reflection peak at 530 nm to 600 nm is 20 nm to 95 nm.

[0031] [4] The linearly polarized light reflective film according to any one of [1] to [3], wherein

[0032] The selective reflection layer is composed of two or more light reflection layers.

[0033] The light reflecting layers having any one of the first reflection peak, the second reflection peak, and the third reflection peak are in contact with each other.

[0034] [5] The linearly polarized light reflective film according to any one of [1] to [4], wherein

[0035] The difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is 0.03 to 0.2.

[0036] [6] The linearly polarized light reflective film according to any one of [1] to [5], wherein

[0037] The difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is 0.05 to 0.14.

[0038] [7] The linearly polarized light reflective film according to any one of [1] to [6], wherein

[0039] The difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is 0.05 to 0.10.

[0040] [8] A windshield having the linearly polarized light reflecting film according to any one of [1] to [7] between a first glass plate and a second glass plate.

[0041] [9] A head-up display system comprising the windshield described in [8] and a projector for irradiating p-polarized light projection image light toward the windshield.

[0042] Effects of the Invention

[0043] According to the present invention, a linearly polarized light reflective film, a windshield, and a head-up display system having high visible light transmittance and good transparency capable of improving the brightness and color of a displayed image can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram showing an example of the linearly polarized light reflecting film of the present invention.

[0045] Figure 2 Observed from the front Figure 1 Schematic diagram of a linearly polarized light reflecting film.

[0046] Figure 3 This is a graph showing the relationship between wavelength and transmittance.

[0047] Figure 4 This is a graph showing the relationship between wavelength and transmittance.

[0048] Figure 5 This is a schematic diagram showing an example of a head-up display including the linearly polarized light reflective film of the present invention.

[0049] Figure 6 This is a schematic diagram showing an example of a windshield having the linearly polarized light reflecting film of the present invention. DETAILED DESCRIPTION

[0050] Hereinafter, the linearly polarized light reflective film, windshield, and head-up display system of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

[0051] In addition, the drawings described below are illustrative drawings for explaining the present invention, and the present invention is not limited to the drawings shown below.

[0052] In addition, the following "to" indicating a numerical range includes the values on both sides. For example, if ε1 is a value α1 to a value β1, this means that the range of ε1 includes the values α1 and β1. In mathematical notation, this is α1≤ε1≤β1.

[0053] Unless otherwise specified, angles such as “angles represented by specific numerical values”, “parallel”, “perpendicular” and “orthogonal” include the error range generally allowed in the applicable technical field.

[0054] In addition, “the same” includes the error range generally allowed in the relevant technical field, and “the entire surface” and the like also include the error range generally allowed in the applicable technical field.

[0055] Unless otherwise specified, the term "light" refers to visible and natural (unpolarized) light. Visible light is the electromagnetic spectrum visible to the human eye, typically denoting wavelengths between 380 and 780 nm. Invisible light is light with wavelengths below 380 nm or above 780 nm.

[0056] Not limited to this, light in the wavelength range of 420 to 490 nm in visible light 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.

[0057] "Visible light transmittance" is defined as the visible light transmittance using illuminant A as specified in JIS (Japanese Industrial Standards) R 3212:2015 (Test methods for automotive safety glass). Specifically, the transmittance at each wavelength in the range of 380 to 780 nm is measured using a spectrophotometer using illuminant A. The transmittance at each wavelength is then multiplied by a weighting coefficient derived from the wavelength distribution and wavelength interval of the brightness-adapted standard luminous efficiency defined by the CIE (International Commission on Illumination) and the resulting weighted average.

[0058] Only when referring to "reflected light" or "transmitted light", it is used to include scattered light and diffracted light.

[0059] P-polarized light is polarized light that oscillates parallel to the plane of incidence. The plane of incidence is the plane perpendicular to the reflecting surface (such as the windshield) and includes both the incident and reflected light rays. In p-polarized light, the plane of vibration of the electric field vector is parallel to the plane of incidence.

[0060] The front retardation is measured using an AxoScan manufactured by Axometrics. Unless otherwise specified, the measurement wavelength is 550 nm. The front retardation can also be measured using a KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments) by incident light within the visible wavelength range along the normal direction of the film. The measurement wavelength can be selected by manually changing the wavelength selection filter or converting the measured value using a program.

[0061] The "projected image" is not the surrounding scenery in front of you, but an image projected by light from a projector. When viewed by an observer, the projected image appears as a visible virtual image floating in front of the linearly polarized light reflecting film on the windshield.

[0062] "Screen image" refers to an image displayed on a rendering device of a projector or an image rendered on an intermediate image screen etc. by a rendering device. A screen image is a real image as opposed to a virtual image.

[0063] The image and the projected image may both be monochrome images, or may be multi-color images of two or more colors, or may be full-color images.

[0064] [Linearly polarized light reflective film]

[0065] Linearly polarized light reflecting film of the present invention

[0066] It has a selective reflection layer formed by laminating an optically anisotropic layer and an isotropic layer,

[0067] The selective reflection layer satisfies all of the following conditions (i) to (iii):

[0068] (i) having at least one first reflection peak with a central reflection wavelength of 430 nm or more and less than 500 nm, and a natural light reflectivity of 10% or more and 20% or less in the first reflection peak

[0069] (ii) having at least one second reflection peak with a central reflection wavelength of 530 nm or more and less than 600 nm, and a natural light reflectivity in the second reflection peak of 10% or more and 20% or less

[0070] (iii) having a third reflection peak with a central reflection wavelength of 600 nm to 800 nm, and the third reflection peak satisfies any of the following conditions:

[0071] (a) It has two or more reflection peaks, and the natural light reflectivity is 10% or more and 20% or less.

[0072] (b) There is one reflection peak, the natural light reflectance is 10% to 20%, and the wavelength bandwidth of the region where the reflectance is higher than the average of the maximum and minimum reflectances at 600 nm to 800 nm is 120 nm or more.

[0073] Figure 1 Schematic diagram showing an example of the linearly polarized light reflecting film of the present invention. Figure 1 As shown, the linearly polarized light reflecting film 10 includes a selective reflection layer formed by alternately laminating optically anisotropic layers (11a, 12a, 13a) and isotropic layers (11b, 12b, 13b). In the illustrated example, the linearly polarized light reflecting film 10 includes a first laminated portion 11 formed by alternately laminating optically anisotropic layers 11a and isotropic layers 11b, a second laminated portion 12 formed by alternately laminating optically anisotropic layers 12a and isotropic layers 12b, and a third laminated portion 13 formed by alternately laminating optically anisotropic layers 13a and isotropic layers 13b.

[0074] The thicknesses of the optically anisotropic layer and the isotropic layer are different among the first laminated part 11, the second laminated part 12, and the third laminated part 13. In addition, the number of laminated layers, the refractive index, etc. may also be different.

[0075] In the linearly polarized light reflective film of the present invention, the refractive index n in the slow axis direction of the optically anisotropic layer is e1 Greater than the refractive index n of the isotropic layer o2 , the refractive index n in the direction perpendicular to the slow axis of the optically anisotropic layer o1 The refractive index n of the isotropic layer o2 The slow axes of the multiple optically anisotropic layers are stacked in parallel. Figure 2 As shown, in a certain direction (in Figure 2 In the vertical direction), the refractive index (n e1 ) layers with high refractive index (n o2 On the other hand, in a direction perpendicular to the one direction (in Figure 2 In the left-right direction), layers with the same refractive index are stacked.

[0076] It is known that a film formed by alternately stacking layers with low refractive index (low refractive index layers) and layers with high refractive index (high refractive index layers) reflects light of a specific wavelength due to structural interference between a large number of low refractive index layers and high refractive index layers. Figure 1 and Figure 2 The linearly polarized light reflecting film shown reflects Figure 2 It can transmit linear polarized light in the vertical direction and allow linear polarized light in the horizontal direction to pass through.

[0077] Here, the reflection spectrum of the linearly polarized light reflective film of the present invention satisfies the above-mentioned items (i) to (iii).

[0078] In a selective reflection layer formed by laminating a low refractive index layer and a high refractive index layer, the reflected wavelength and reflectivity can be adjusted by adjusting the refractive index difference between the low refractive index layer and the high refractive index layer, the thickness, the number of laminations, etc. Figure 1 In the example shown, the reflection satisfying item (i) is mainly realized by the first laminated portion 11 , the reflection satisfying item (ii) is realized by the second laminated portion 12 , and the reflection satisfying item (iii) is realized by the third laminated portion 13 .

[0079] exist Figure 3 and Figure 4 Examples of natural light reflection spectra satisfying the above items (i) to (iii) are shown in FIG.

[0080] Figure 3 The spectrum shown in the graph has a first reflection peak near a wavelength of 450 nm. The natural light reflectance at this first reflection peak is 10% to 20%, satisfying the item (i).

[0081] in addition, Figure 3 The spectrum shown in the graph has a second reflection peak near a wavelength of 530 nm. The natural light reflectance of this second reflection peak is 10% to 20%, which satisfies the condition (ii).

[0082] also, Figure 3 The spectrum shown in the graph has two third reflection peaks at wavelengths of 640 nm and 700 nm. The natural light reflectances at these third reflection peaks are 10% or more and 20% or less, respectively, satisfying (a) of item (iii).

[0083] on the other hand, Figure 4 The spectrum shown in the graph has a first reflection peak at around a wavelength of 460 nm. The natural light reflectance at this first reflection peak is 10% to 20%, satisfying the item (i).

[0084] in addition, Figure 4 The spectrum shown in the graph has a second reflection peak near a wavelength of 530 nm. The natural light reflectance of this second reflection peak is 10% to 20%, which satisfies the condition (ii).

[0085] In addition, Figure 4 The spectrum shown in the graph has a third reflection peak near a wavelength of 690 nm. The average of the maximum and minimum reflectance values of this third reflection peak in the wavelength band from 600 nm to 800 nm is 16.6%. The wavelength bandwidth of the region where the reflectance exceeds this value is 150 nm, satisfying item (iii) (b).

[0086] In the present invention, the reflection peak is defined as a peak having a maximum value with a difference of 2% or more from an adjacent minimum value and a half-value width of 10 to 200 nm.

[0087] As mentioned above, automotive head-up display systems require a transparent appearance from all angles, both to meet legally required transmittance requirements and to maintain design quality. To maintain the legally required transmittance of 70% or higher and achieve a near-transparent (white) appearance, reducing reflectivity has been considered. However, excessively reducing reflectivity reduces the brightness of the displayed (projected) image, impairing visibility.

[0088] In contrast, the linearly polarized light reflective film of the present invention exhibits a second reflection peak with a reflectivity of 10% to 20% at a wavelength of 530nm to less than 600nm, thereby enhancing color transparency. To ensure the legally required 70% frontal transmittance, reflectivity near the visually sensitive 550nm wavelength is crucial. Therefore, by setting the reflectivity of the second reflection peak to 20% or less, transmittance can be ensured. Next, to enhance brightness, a higher reflectivity near 550nm is required in an oblique direction (at an incident angle of 60°). By exhibiting a third reflection peak with a reflectivity of 10% to 20% at a wavelength of 600nm to 800nm, having two reflection peaks, or having a reflection band width of 120nm or more, the linearly polarized light reflective film of the present invention can enhance frontal brightness of displayed images and improve color transparency when viewed from an oblique direction (at an incident angle of 60°). Furthermore, the frontal reflection color varies from yellow to red only at the second and third reflection peaks. Therefore, the linearly polarized light reflective film of the present invention has a first reflection peak with a reflectivity of 10% to 20% at a wavelength of 430 nm to less than 500 nm, thereby improving the color transparency when viewed from the front (at an incident angle of 5°). Furthermore, by providing the three reflection peaks, wavelength bands with low reflectivity are formed between the first and second reflection peaks, and between the second and third reflection peaks, thereby improving transmittance.

[0089] These effects enable windshields with linearly polarized light reflective films sandwiched between green glass to achieve a natural light transmittance of 70% or higher (80% or higher when using clear glass). Furthermore, the P-polarized light reflectance can be increased to 25% or higher, improving the brightness of displayed images. Furthermore, the color transparency can be enhanced when viewed from all directions.

[0090] As described above, the wavelength and reflectivity reflected by the selective reflection layer can be adjusted by adjusting the refractive index difference between the low-refractive index layer and the high-refractive index layer, the thickness, the number of layers, and the like. Specifically, by setting the thickness d of the low-refractive index layer and the high-refractive index layer to d = λ / (4×n) based on the wavelength λ of the reflected light and the refractive index n, the wavelength λ of the reflected light can be adjusted. In addition, since the reflectivity increases with the number of low-refractive index layers and high-refractive index layers stacked, the reflectivity can be adjusted by adjusting the number of layers stacked. Furthermore, the width of the reflection band can be adjusted by adjusting the refractive index difference between the low-refractive index layer and the high-refractive index layer.

[0091] From the perspective of improving the apparent color, it is preferable that the intensity ratio (reflectance ratio) between the first and second reflection peaks is 80% to 120%, the intensity ratio between the first and third reflection peaks is 80% to 120%, and the intensity ratio between the second and third reflection peaks is 80% to 120%. When the reflectances at the respective reflection peaks are close, the apparent color approaches white, which can improve transparency.

[0092] The bandwidth of each reflection peak depends on the difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer. The larger the refractive index difference, the larger the bandwidth. Furthermore, if reflection peaks with low reflectivity are located at close wavelengths, interference may occur, causing the reflection peaks to become too strong or too weak. From the perspective of appropriately adjusting the bandwidth of each reflection peak, improving the brightness of the displayed image while increasing the transmittance, and reducing the influence of interference with adjacent reflection peaks, the difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is preferably 0.03 to 0.2, more preferably 0.05 to 0.14, and even more preferably 0.05 to 0.10.

[0093] In addition, in the first reflection peak, the wavelength bandwidth of the region where the reflectivity is higher than the average of the maximum and minimum reflectivity values at 430nm to 500nm is preferably greater than 20nm and less than 95nm, more preferably greater than 25nm and less than 85nm, and further preferably greater than 30nm and less than 80nm.

[0094] Similarly, in the second reflection peak, the wavelength bandwidth of the region where the reflectivity is higher than the average of the maximum and minimum reflectivity values at 530 nm to 600 nm is preferably greater than 20 nm and less than 95 nm, more preferably greater than 25 nm and less than 85 nm, and further preferably greater than 30 nm and less than 80 nm.

[0095] The wavelength bandwidth of the first reflection peak and the wavelength bandwidth of the second reflection peak are respectively not less than 20nm and not more than 95nm, that is, the wavelength bandwidth of the first reflection peak and the second reflection peak are narrow bands, thereby improving the front brightness of the displayed image and at the same time improving the transmittance.

[0096] In addition, Figure 3 and Figure 4 In the example shown, the configuration is such that there is one first reflection peak and one second reflection peak respectively. However, there may be two or more first reflection peaks and two or more second reflection peaks respectively.

[0097] In addition, it is preferable that the selective reflection layer is composed of two or more light reflection layers having different selective reflection wavelengths, and the light reflection layers having any one of the first reflection peak, the second reflection peak, and the third reflection peak are in contact with each other. Figure 1 In the example shown, the first laminated section 11, which selectively reflects light having a wavelength of the first reflection peak, and the second laminated section 12, which selectively reflects light having a wavelength of the second reflection peak, are in contact with each other. Furthermore, the second laminated section 12, which selectively reflects light having a wavelength of the second reflection peak, and the third laminated section 13, which selectively reflects light having a wavelength of the third reflection peak, are in contact with each other. The first laminated section 11, the second laminated section 12, and the third laminated section constitute the light-reflecting layers of the present invention.

[0098] If the light-reflecting layers having any of the reflection peaks are separated from each other, the film thickness between the layers becomes thick, making it difficult to achieve the interference effect of light reflected by each light-reflecting layer. In contrast, by configuring the light-reflecting layers to be in contact with each other, the wavelength bandwidth of each reflection peak can be narrowed by utilizing the interference effect of light reflected by each light-reflecting layer.

[0099] The linearly polarized light reflecting film may be in the form of a film or sheet, etc. The linearly polarized light reflecting film may be formed into a roll, etc., as a film before being applied to a windshield.

[0100] The selective reflector layer can be made of materials and methods described in, for example, Japanese Patent Publication No. 9-506837. Specifically, a wide variety of materials can be used to form the selective reflector layer, provided the processing is performed under conditions selected to achieve a refractive index relationship. Generally, the first material must have a different refractive index from the second material in the selected direction. This refractive index difference can be achieved through various methods, including stretching, extrusion molding, or coating during or after film formation. Furthermore, the two materials preferably have similar rheological properties (e.g., melt viscosity) to enable simultaneous extrusion.

[0101] As for materials particularly suitable for use as the selective reflection layer, as optically anisotropic layers, PEN (polyethylene naphthalate) and PET (polyethylene terephthalate) can be cited, and as isotropic layers, PEN, PET and PMMA (polymethyl methacrylate resin) (adjusted to be isotropic) can be cited.

[0102] As described above, the linearly polarized light reflective film (selective reflection layer) of the present invention comprises three laminated sections of optically anisotropic layers and isotropic layers having different thicknesses, in order to form a structure having first, second, and third reflection peaks. In the present invention, the three laminated sections are formed separately by stretching, extrusion molding, or the like, and then the laminated sections are bonded together to produce the linearly polarized light reflective film. Alternatively, the pre-processing thickness can be adjusted to form three laminated sections of varying thicknesses, and the three laminated sections can be integrally formed by stretching, extrusion molding, or the like.

[0103] The thickness of the selective reflection layer is preferably in the range of 2.0 to 50 μm, more preferably in the range of 8.0 to 30 μm.

[0104] The linearly polarized light reflective film is a linearly polarized light reflective film having a selective reflection layer. The linearly polarized light reflective film may also have a structure including a phase difference layer, a polarization conversion layer, a support, and an adhesive layer in addition to the selective reflection layer.

[0105] Preferably, the support, adhesive layer, etc. are all transparent in the visible light region.

[0106] Furthermore, it is preferred that the support, adhesive layer, etc. all have low birefringence. Low birefringence means that the front retardation is 10 nm or less within the wavelength range in which the linearly polarized light reflective film of the windshield of the present invention reflects. This front retardation is preferably 5 nm or less. Furthermore, it is preferred that the difference in refractive index between the support, adhesive layer, etc. and the average refractive index (in-plane average refractive index) of the selective reflection layer be small.

[0107] (Support)

[0108] The support can also serve as a substrate for forming the selective reflective layer. The support used to form the selective reflective layer can also be a temporary support that is removed after the selective reflective layer is formed. Therefore, the completed linearly polarized light reflective film or windshield may not include a support. Furthermore, when the completed linearly polarized light reflective film or windshield includes a support other than the support that is removed as a temporary support, the support is preferably transparent in the visible light region.

[0109] The material of the support is not limited. Examples of the support include polyesters such as polyethylene terephthalate (PET), polycarbonates, acrylic resins, epoxy resins, polyurethanes, polyamides, polyolefins, cellulose derivatives, and plastic films such as silicone. In addition to the aforementioned plastic films, glass may also be used as a temporary support.

[0110] The thickness of the support may be approximately 5.0 to 1000 μm, preferably 10 to 250 μm, and more preferably 15 to 90 μm.

[0111] Next, a windshield and a head-up display (HUD) including the linearly polarized light reflective film of the present invention will be described.

[0112] <Windshield>

[0113] By using the linearly polarized light reflective film of the present invention, a windshield having a projected image display function can be provided.

[0114] Windshield refers to the general window glass and windshield of vehicles such as cars and trains, airplanes, ships, motorcycles, and amusement rides. The windshield is preferably used as the front windshield and windshield in the forward direction of the vehicle.

[0115] The visible light transmittance of the windshield is not limited, but a high visible light transmittance is preferred. The visible light transmittance of the windshield is preferably 70% or higher, more preferably exceeding 70%, further preferably 75% or higher, and particularly preferably 80% or higher.

[0116] The above-mentioned visible light transmittance is preferably satisfied at any location on the windshield, and is particularly preferably satisfied at locations where the linearly polarized light reflective film is present. As described above, the linearly polarized light reflective film of the present invention has a high visible light transmittance, and thus can be configured to satisfy the above-mentioned visible light transmittance regardless of the type of glass commonly used for the windshield.

[0117] The shape of the windshield is not limited and can be appropriately determined depending on the object for which the windshield is to be installed. For example, the windshield can be flat or three-dimensional with curved surfaces such as concave or convex surfaces. In a windshield formed for a vehicle in which it is to be used, the surface facing upward during normal use and the side visible to the viewer, driver, or interior of the vehicle can be specified.

[0118] The thickness of the windshield in the portion where the linearly polarized light reflecting film is disposed may be uniform or non-uniform. For example, the windshield may have a wedge-shaped cross-section, as in the vehicle glass disclosed in JP-A-2011-505330, and the thickness of the linearly polarized light reflecting film may be non-uniform. However, it is preferred that the thickness of the windshield in the portion where the linearly polarized light reflecting film is disposed be uniform.

[0119] In the windshield, the linearly polarized light reflecting film may be provided at the projection image display portion (projection image reflecting portion) of the windshield.

[0120] By providing the linearly polarized light reflective film of the present invention on the outer surface of a windshield glass plate, or, as described below, between glass panels of a windshield having a laminated glass structure, a head-up display (hereinafter also referred to as HUD) using the windshield can be constructed.

[0121] When the linearly polarized light reflecting film of the present invention is provided on the outer surface of the glass plate of the windshield, the linearly polarized light reflecting film may be provided inside the vehicle (on the incident side of the projected image) or outside, but is preferably provided inside.

[0122] Furthermore, the linearly polarized light reflective film of the present invention has lower scratch resistance than glass sheets. Therefore, when the windshield is a laminated glass structure, it is more preferable to place the linearly polarized light reflective film between the two sheets of glass constituting the laminated glass in order to protect the reflective film.

[0123] As described above, the linearly polarized light reflecting film is a member for displaying a projected image by reflecting the projected image. Therefore, the linearly polarized light reflecting film may be provided at a position where the projected image projected from a projector or the like can be displayed in a visible manner.

[0124] In other words, the linearly polarized light reflective film of the present invention functions as a combiner in a HUD. In a HUD, a combiner is an optical component that visually displays an image projected from a projector, and that simultaneously displays information such as scenery on the opposite side of the projected light's incidence when the combiner is viewed from the projected image's incident side. In other words, the combiner functions as an optical path combiner, combining ambient light with the projected image's light for display.

[0125] The linearly polarized light reflecting film may be provided on the entire surface of the windshield or on a portion of the windshield in the plane direction, but is preferably provided on a portion of the windshield.

[0126] When a linearly polarized light reflective film is applied to a portion of the windshield, the film can be applied anywhere on the windshield. However, when used as a HUD, it is preferably positioned so that the virtual image appears at a location that is easily visible to an observer such as the driver. For example, the location of the linearly polarized light reflective film on the windshield can be determined based on the relationship between the position of the driver's seat in a HUD-equipped vehicle and the location of the projector.

[0127] The linear polarization reflective film may be flat without a curved surface, or may have a curved surface. In addition, the linear polarization reflective film may have a concave or convex shape as a whole to magnify or reduce the projected image.

[0128] [Laminated glass]

[0129] The windshield may also have a laminated glass structure. The windshield of the present invention is a laminated glass having the above-mentioned linearly polarized light reflecting film of the present invention between a first glass plate and a second glass plate.

[0130] The windshield may have a structure in which a linearly polarized light reflecting film is disposed between the first glass plate and the second glass plate. However, the windshield preferably has an intermediate film (intermediate film sheet) disposed between at least one of the first glass plate and the linearly polarized light reflecting film and between the linearly polarized light reflecting film and the second glass plate.

[0131] In a windshield, for example, the first glass plate is positioned on the side of the HUD opposite to the side where the image is viewed (the vehicle's exterior), while the second glass plate is positioned on the side where the image is viewed (the vehicle's interior). In the windshield of the present invention, the designations "first" and "second" have no technical significance and are provided for the purpose of distinguishing the two glass plates. Therefore, the first glass plate may be positioned on the vehicle's interior side, while the second glass plate may be positioned on the vehicle's exterior side.

[0132] Glass sheets commonly used for windshields can be used for the first and second glass sheets. For example, glass sheets having a visible light transmittance of 80% or less, such as 73% or 76%, or other glass sheets with high heat insulation properties, can also be used. Even when using glass sheets with such low visible light transmittance, the use of the linearly polarized reflective film of the present invention allows the production of a windshield having a visible light transmittance of 70% or more at the location of the linearly polarized reflective film.

[0133] The thickness of the glass plate is not particularly limited and 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 first and second glass plates may be made of the same material or have different thicknesses.

[0134] The windshield having a laminated glass structure can be manufactured using a known laminated glass manufacturing method.

[0135] Generally, laminated glass can be produced by sandwiching an interlayer film between two glass plates, repeating multiple heating and pressurizing treatments (such as treatment using rubber rollers), and finally performing a heating treatment under pressurized conditions using an autoclave or the like.

[0136] As an example, a windshield having a laminated glass structure having a linearly polarized light reflective film and an intermediate film can be produced by the above-mentioned method for producing laminated glass after forming the linearly polarized light reflective film on the surface of the glass plate, or can be produced by the above-mentioned method for producing laminated glass using an intermediate film for laminated glass including the above-mentioned linearly polarized light reflective film.

[0137] When a linearly polarized light reflecting film is formed on a surface of a glass plate, the glass plate on which the linearly polarized light reflecting film is provided may be the first glass plate or the second glass plate. In this case, the linearly polarized light reflecting film is bonded to the glass plate using, for example, an adhesive.

[0138] (Intermediate Film)

[0139] As the interlayer film (interlayer sheet), any known interlayer film used as an interlayer (interlayer) in laminated glass can be used. For example, a resin film containing a resin selected from the group consisting of polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, and chlorine-containing resin can be used. These resins are preferably the main component of the interlayer film. The main component refers to a component that accounts for 50% by mass or more of the interlayer film.

[0140] Among the above resins, polyvinyl butyral and ethylene-vinyl acetate copolymer are preferred, and polyvinyl butyral is more preferred. The resin is preferably a synthetic resin.

[0141] Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol with butyraldehyde. The preferred lower limit of the acetalization degree of the polyvinyl butyral is 40%, the preferred upper limit is 85%, the more preferred lower limit is 60%, and the more preferred upper limit is 75%.

[0142] Polyvinyl alcohol is generally obtained by saponifying polyvinyl acetate, and polyvinyl alcohol having a saponification degree of 80 to 99.8 mol % is generally used.

[0143] The preferred lower limit of the degree of polymerization of the polyvinyl alcohol is 200, and the preferred upper limit is 3000. If the degree of polymerization of the polyvinyl alcohol is 200 or higher, the penetration resistance of the resulting laminated glass is unlikely to decrease. If it is 3000 or lower, the formability of the resin film is improved, and the rigidity of the resin film is not excessively increased, resulting in good processability. The more preferred lower limit is 500, and the more preferred upper limit is 2000.

[0144] (Intermediate film including linearly polarized light reflecting film)

[0145] An interlayer film for laminated glass comprising a linearly polarized light reflective film can be formed by laminating the linearly polarized light reflective film to the surface of the aforementioned interlayer film. Alternatively, the linearly polarized light reflective film can be sandwiched between two of the aforementioned interlayer films. The two interlayer films may be identical or different, but are preferably identical.

[0146] The linearly polarized light reflecting film and the interlayer film can be laminated using a known lamination method, but a press bonding process is preferably used. The press bonding process is preferably carried out under a certain degree of heating and pressure so that the laminate and the interlayer film do not separate after processing.

[0147] In order to perform stable pressure bonding, the film surface temperature of the interlayer film on the bonding side is preferably 50 to 130°C, more preferably 70 to 100°C.

[0148] It is preferred to apply pressure during lamination. The pressure conditions are not limited, but it is preferably less than 2.0 kg / cm 2 (less than 196 kPa), more preferably 0.5 to 1.8 kg / cm2 (49 to 176 kPa), more preferably 0.5 to 1.5 kg / cm 2 (49 to 147 kPa).

[0149] In addition, when the linearly polarized light reflection film has a support, the support can be peeled off simultaneously with the lamination, or after the lamination, or before the lamination. That is, the linearly polarized light reflection film pasted on the intermediate film obtained after lamination may also have no support.

[0150] An example of the method for manufacturing an intermediate film including a linearly polarized light reflection film includes:

[0151] (1) The first step of laminating the linearly polarized light reflection film on the surface of the first intermediate film to obtain a first laminate; and

[0152] (2) The second step of laminating the second intermediate film on the surface of the linearly polarized light reflection film in the first laminate, which is opposite to the surface on which the first intermediate film is laminated.

[0153] For example, in the first step, the support is not opposed to the first intermediate film, and the linearly polarized light reflection film is laminated on the first intermediate film. Next, the support is peeled off from the linearly polarized light reflection film. Further, in the second step, the second intermediate film is laminated on the surface from which the support has been peeled off. Thus, an intermediate film including a linearly polarized light reflection film without a support can be manufactured. In addition, by using the intermediate film including this linearly polarized light reflection film, it is possible to easily produce laminated glass in which the linearly polarized light reflection film has no support.

[0154] In order to stably peel off the support without breakage or the like, the temperature of the support when peeling off the support from the linearly polarized light reflection film is preferably 40°C or higher, more preferably 40 to 60°C.

[0155] <HUD (Head-Up Display System)>

[0156] The windshield can be used as a component of the HUD. The HUD preferably includes a projector.

[0157] [Projector]

[0158] A "projector" is a "device for projecting light or an image", which includes a "device for projecting a drawn image" and emits projection light carrying the displayed image. In the HUD of the present invention, the projector emits projection light of p-polarized light.

[0159] In the HUD, the projector is arranged so that the projection light of p-polarized light carrying the displayed image can be incident on the linearly polarized light reflection film in the windshield at an inclined incident angle.

[0160] In the HUD, it is preferable that the projector includes a rendering device and reflects and displays an image (real image) rendered on a small intermediate image screen as a virtual image via a combiner.

[0161] The projector may be any known projector used for HUDs, as long as it can emit p-polarized light. In addition, it is preferable that the imaging distance of the virtual image of the projector, that is, the imaging position of the virtual image, is variable.

[0162] As methods for changing the imaging distance of the virtual image of the projector, for example, there can be cited a method of moving the image generation surface (screen) (refer to Japanese Patent Gazette No. 2017-21302), a method of switching between multiple optical paths with different optical path lengths (refer to WO2015 / 190157), a method of changing the optical path length by inserting and / or moving a reflector, a method of changing the focal length by using a group lens as an imaging lens, a method based on the movement of the projector 22, a method of switching between multiple projectors with different imaging distances of virtual images, and a method of using a variable focus lens (refer to WO2010 / 116912), etc.

[0163] Furthermore, the projector may be a projector in which the imaging distance of the virtual image can be continuously changed, or a projector in which the imaging distance of the virtual image can be switched at two points or three or more points.

[0164] Here, it is preferred that the imaging distances of at least two virtual images of the projected light formed by the projector differ by at least 1 meter. Therefore, if the projector is capable of continuously changing the imaging distance of the virtual images, it is preferred that the imaging distance of the virtual images be adjustable by at least 1 meter. Using such a projector is preferred because it can appropriately address situations where the driver's line of sight differs significantly, such as when driving at normal speeds on a regular road and when driving at high speeds on a highway.

[0165] (Drawing Device)

[0166] The drawing device may be a device that displays images itself or a device that emits light capable of drawing images.

[0167] In a rendering device, light from a light source is modulated using a rendering method such as a light modulator, a laser intensity modulation unit, or a light deflection unit for rendering. A rendering device is a device that includes a light source and, depending on the rendering method, a light modulator, a laser intensity modulation unit, or a light deflection unit for rendering.

[0168] (light source)

[0169] The light source is not limited, and known light sources used for projectors, drawing equipment, displays, and the like, such as LEDs (light emitting diodes), organic light emitting diodes (OLEDs), discharge tubes, and laser light sources, can be used.

[0170] Among these, LEDs and discharge tubes are preferred as light sources for drawing devices that emit linearly polarized light, with LEDs being particularly preferred. This is because LEDs emit discontinuous wavelengths in the visible light region, making them suitable for combination with a combiner using a cholesteric liquid crystal layer that exhibits selective reflection within a specific wavelength range, as described later.

[0171] (Drawing method)

[0172] There is no particular limitation on the drawing method, and the method can be selected according to the light source used, etc.

[0173] Examples of rendering methods include LCD (Liquid Crystal Display) and LCOS (Liquid Crystal on Silicon) methods using fluorescent display tubes and liquid crystals, DLP (registered trademark) (Digital Light Processing), and scanning methods using lasers. Alternatively, a fluorescent display tube integrated with a light source may be used. The LCD method is preferred.

[0174] In the LCD and LCOS systems, light of each color is modulated and combined by a light modulator, and then emitted from a projection lens.

[0175] The DLP method uses a display system that uses a DMD (Digital Micromirror Device), which uses micromirrors with the same number of pixels to draw the image, and light is emitted from a projection lens.

[0176] The scanning method uses light to scan across a screen, creating an image using afterimages in the eye. For example, see Japanese Patent Application Publication Nos. 7-270711 and 2013-228674. In the laser scanning method, intensity-modulated laser light of various colors, such as red, green, and blue, is combined into a single beam using a combining optical system or a focusing lens. This beam is then scanned by a light deflection unit and drawn onto an intermediate image screen (described later).

[0177] In the scanning method, for example, the brightness modulation of each color laser of red light, green light, and blue light can be performed directly as a change in the intensity of the light source, or it can be performed through an external modulator. As the light deflection unit, galvanometer mirrors, a combination of galvanometer mirrors and polygonal mirrors, and MEMS (Micro Electro Mechanical Systems) can be mentioned, among which MEMS is preferred. As the scanning method, random scanning and raster scanning can be mentioned, but raster scanning is preferably used. In the raster scanning method, for example, the laser can be driven at a resonant frequency in the horizontal direction and at a sawtooth wave in the vertical direction. Since the scanning method does not require a projection lens, it is easier to miniaturize the device.

[0178] The light emitted from the drawing device may be linearly polarized light or natural light (non-polarized light).

[0179] Drawing devices using LCD or LCOS methods, as well as those using laser light sources, inherently emit linearly polarized light. For drawing devices that emit linearly polarized light and include multiple wavelengths (colors), the polarization directions (transmission axis directions) of the multiple wavelengths are preferably the same. Some commercially available drawing devices are known to have uneven polarization directions within the wavelength ranges of red, green, and blue light (see Japanese Patent Application Laid-Open No. 2000-221449). Specifically, examples are known in which the polarization direction of green light is orthogonal to that of red and blue light.

[0180] Furthermore, in the HUD of the present invention, as described above, the projection light emitted by the projector is p-polarized light.

[0181] (Intermediate Image Screen)

[0182] As mentioned above, the rendering device can also use an intermediate image screen. An "intermediate image screen" is a screen on which images are rendered. Specifically, when the light emitted from the rendering device is not yet visually recognizable as an image, the rendering device uses this light to form a recognizable image on the intermediate image screen. The image rendered on the intermediate image screen can be projected onto the combiner by light passing through the intermediate image screen or by light reflected from the intermediate image screen.

[0183] 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 intensity of polarized light incident on the intermediate image screen will be disturbed, which can easily cause color unevenness in the combiner (linearly polarized light reflective film). However, using a retardation film with a predetermined phase difference can reduce this color unevenness.

[0184] An intermediate image screen preferably has the function of diffusing and transmitting incident light. This allows for magnified display of the projected image. Examples of such intermediate image screens include those composed of a microlens array. Microlens arrays used in HUDs are described, for example, in Japanese Patent Application Laid-Open Nos. 2012-226303, 2010-145745, and 2007-523369.

[0185] The projector may also include a reflecting mirror or the like for adjusting the optical path of the projection light formed by the drawing device.

[0186] For HUDs using a windshield as a linearly polarized light reflective film, reference may be made to Japanese Patent Application Laid-Open Nos. 2-141720, 10-96874, and 2003-98470, U.S. Patent No. 5,013,134, and JP-A-2006-512622.

[0187] Windshields are particularly useful for HUDs used in conjunction with projectors using lasers, LEDs, OLEDs (organic light-emitting diodes), or other light sources whose emission wavelengths are discontinuous in the visible light region. This is because the center wavelength of the selective reflection of the cholesteric liquid crystal layer can be adjusted according to the emission wavelength. Furthermore, they can be used for projection on displays such as LCDs (liquid crystal displays) that display polarized light.

[0188] [Projection light (incident light)]

[0189] The incident light preferably enters the linearly polarized light reflective film at an oblique angle of incidence of 45° to 70° relative to the normal line. 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 injecting p-polarized light within this angle range, the selective reflection layer for incident light used for projected image display reduces the amount of light reflected from the windshield surface on the viewing side, enabling image display with minimal ghosting.

[0190] The above angle is also preferably 50° to 65°. In this case, the following structure is sufficient: the projected image can be observed at an angle of 45° to 70°, preferably 50° to 65°, relative to the normal line of the selective reflection layer on the side opposite to the incident light.

[0191] Incident light may also enter from any direction of the windshield, such as up, down, left, and right, and may be determined in accordance with the visual recognition direction. For example, it is preferable that the incident light enters from the bottom direction at the above-mentioned oblique incident angle during use.

[0192] In addition, the linearly polarized light reflecting film of the windshield only needs to be arranged so as to reflect incident p-polarized light.

[0193] As described above, the projection light used when displaying a projected image in the HUD of the present invention is p-polarized light that vibrates in a direction parallel to the incident plane.

[0194] If the projector's output light is not linearly polarized, p-polarized light can be formed by installing a linear polarizing film (polarizer) on the projector's output side. Alternatively, p-polarized light can be formed by using a known method such as a linear polarizing film in the optical path from the projector to the windshield. In this case, components that convert non-linearly polarized projection light into p-polarized light are also considered components of the projector in the HUD of the present invention.

[0195] As described above, for a projector whose polarization direction of outgoing light is non-uniform in the wavelength ranges of red, green, and blue light, it is preferable to adjust the polarization direction in a wavelength-selective manner so that it is incident as p-polarized light in the wavelength ranges of all colors.

[0196] As described above, the HUD (projector) may be a projection system that can change the position of the virtual image. By making the position of the virtual image changeable, the driver can visually recognize the virtual image more comfortably and conveniently.

[0197] The virtual image formation position is a position where the driver of the vehicle can visually recognize the virtual image, and is, for example, usually a position 1000 mm or more in front of the windshield viewed by the driver.

[0198] Here, if the linear polarization reflective film on the glass is non-uniform (wedge-shaped), as described in the aforementioned Japanese Unexamined Patent Publication No. 2011-505330, the angle of the wedge must also be changed when the virtual image formation position is changed. Therefore, as described in Japanese Unexamined Patent Publication No. 2017-15902, for example, it is necessary to virtually cope with changes in the virtual image formation position by locally changing the angle of the wedge and changing the projection position.

[0199] However, in the HUD of the present invention using the windshield of the present invention and utilizing p-polarized light as described above, since wedge-shaped glass is not required and the thickness of the glass can be made uniform in the linearly polarized light reflective film, a projection system that makes the aforementioned virtual image formation position variable can be appropriately adopted.

[0200] Next, refer to Figure 5 and Figure 6 The HUD will be described in more detail.

[0201] Figure 5 Schematic diagram showing an example of a head-up display including a linearly polarized light reflective film according to an embodiment of the present invention. Figure 6 This is a schematic diagram showing an example of a windshield having a linearly polarized light reflective film according to an embodiment of the present invention.

[0202] The HUD 20 includes a projector 22 and a windshield 24 and is used in a vehicle such as a passenger car.

[0203] In HUD20, if Figure 6 As conceptually shown in FIG, the windshield 24 includes a first glass plate 28 as a first glass plate, a second glass plate 30 as a second glass plate, a linearly polarized light reflecting film 10 , an intermediate film 36 , and an adhesive layer 38 .

[0204] The linearly polarized light reflecting film 10 is Figure 1 The linearly polarized light reflecting film 10 shown in FIG. 1 has a selective reflecting layer formed by alternately laminating optically anisotropic layers and isotropic layers. Figure 2 The linearly polarized light reflecting films 10 shown are arranged so that their axes P coincide with each other. In the windshield (HUD) of the present invention, the linearly polarized light reflecting film may have a support.

[0205] The vertical direction Y of the windshield 24 corresponds to the vertical direction of the vehicle, etc., on which the windshield 24 is installed, and is a direction with the ground side being the lower side and the opposite side being the upper side. Furthermore, when the windshield 24 is installed on a vehicle, etc., it may be tilted for structural or design convenience. In such cases, the vertical direction Y is a direction along the surface 25 of the windshield 24. The surface 25 refers to the outer surface of the vehicle.

[0206] The projector 22 is as described above. Any projector capable of emitting p-polarized projection light carrying the displayed image can be used, and a known projector used for HUDs can be used. Furthermore, the projector 22 preferably has a variable imaging distance, that is, a variable imaging position, of the virtual image.

[0207] In the HUD 20, the projector 22 projects p-polarized light onto the windshield 24 (second glass plate 30). By using p-polarized light as the projection light projected by the projector 22 onto the windshield 24, reflection of the projection light from the second glass plate 30 and the first glass plate 28 of the windshield 24 is significantly reduced, thereby suppressing problems such as the observation of ghosting.

[0208] Preferably, the projector 22 projects p-polarized light onto the windshield at the Brewster angle, thereby eliminating reflection of the projection light on the second glass plate 30 and the first glass plate 28 and enabling a clearer image to be displayed.

[0209] The windshield 24 is a so-called laminated glass, and has an intermediate film 36 , a linearly polarized light reflecting film 10 , and an adhesive layer 38 between a first glass plate 28 and a second glass plate 30 .

[0210] The projection light emitted by the projector 22 enters the surface 30a of the second glass plate 30. The linearly polarized light reflecting film 10 reflects the p-polarized light. As described above, the linearly polarized light reflecting film 10 is set to Figure 2 The axis P shown is the direction of linearly polarized light reflected by the reflective film, so as to reflect p-polarized light.

[0211] As described above, the linearly polarized light reflective film 10 has a first reflection peak, a second reflection peak, and a third reflection peak as reflection characteristics.

[0212] The linearly polarized light reflecting film 10 is bonded to the first glass plate 28 via the intermediate film 36 , and bonded to the second glass plate 30 via the adhesive layer 38 , and is sandwiched between the first glass plate 28 and the second glass plate 30 .

[0213] In the present invention, it is preferred that the first glass plate 28 and the second glass plate 30 of the windshield 24 be arranged substantially parallel to each other.

[0214] The first glass plate 28 and the second glass plate 30 are both known glasses (glass plates) used for windshields of vehicles, etc. Therefore, the forming material, thickness, shape, etc. can be the same as those of known glasses used for windshields. Figure 6 The first glass plate 28 and the second glass plate 30 are both flat, but are not limited thereto. They may be partially curved or the entire surface may be curved.

[0215] The interlayer film 36 prevents glass from penetrating and scattering in the event of an accident, and further serves to bond the linear polarized light reflective film 10 and the first glass plate 28. A known interlayer film (interlayer) used in laminated glass windshields can be used for the interlayer film 36. Examples of materials for forming the interlayer film 36 include polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, chlorine-containing resin, and polyurethane.

[0216] Furthermore, the thickness of the interlayer film 36 is not limited either, and may be set to a thickness corresponding to the forming material and the like, similarly to the interlayer film of a known windshield.

[0217] The adhesive layer 38 is, for example, a layer composed of a coating-type adhesive. The linearly polarized light reflective film 10 is bonded to the second glass plate 30 via the adhesive layer 38. Furthermore, in the windshield of the present invention, the linearly polarized light reflective film 10 may be bonded to the second glass plate 30 via an interlayer film, instead of the adhesive layer 38. Furthermore, if the linearly polarized light reflective film 10 is smaller than the interlayer film 36 used to bond the linearly polarized light reflective film 10 to the first glass plate 28, the interlayer film 36 may be used to bond the linearly polarized light reflective film 10 to the second glass plate 30.

[0218] The adhesive layer 38 is not limited, as long as it can ensure the transparency required for the windshield 24 and can bond the linearly polarized light reflective film 10 to the glass with the required adhesive strength. Adhesive layers composed of various known coating adhesives can be used. The same film as the interlayer film 36, such as PVB, can be used for the adhesive layer 38. Alternatively, an acrylic adhesive can be used for the adhesive layer 38. Furthermore, as shown below, the same adhesive layer as the above-mentioned adhesive layer can be used for the adhesive layer 38.

[0219] The adhesive layer 38 may be formed of an adhesive similar to the above-mentioned adhesive layer.

[0220] Adhesives, based on their curing methods, include hot melt adhesives, thermosetting adhesives, light curing adhesives, reaction curing adhesives, and pressure-sensitive adhesives that do not require curing. Regardless of the adhesive type, materials that can be used include acrylate, urethane, urethane acrylate, epoxy, epoxy acrylate, polyolefin, modified olefin, polypropylene, ethylene vinyl alcohol, vinyl chloride, chloroprene rubber, cyanoacrylate, polyamide, polyimide, polystyrene, and polyvinyl butyral compounds.

[0221] From the viewpoint of workability and productivity, light curing is preferred as the curing method. From the viewpoint of optical transparency and heat resistance, acrylate-based, urethane acrylate-based, and epoxy acrylate-based materials are preferably used.

[0222] The adhesive layer 38 can also be formed using a highly transparent adhesive transfer tape (OCA tape). Commercially available products for image display devices, particularly those for the image display surface of image display devices, can be used as highly transparent adhesive transfer tapes. Examples of commercially available products include adhesive sheets (such as PD-S1) manufactured by Panac Co., Ltd. and MHM series adhesive sheets manufactured by Nichiei Kagaku Co., Ltd.

[0223] There is no limitation on the thickness of the adhesive layer 38. Therefore, the thickness may be appropriately set according to the material forming the adhesive layer 38 so as to obtain sufficient adhesive strength.

[0224] If the adhesive layer 38 is too thick, the linearly polarized light reflecting film 10 may not be bonded to the first glass plate 28 or the second glass plate 30 while maintaining sufficient planarity. In consideration of this, the thickness of the adhesive layer 38 is preferably 0.1 to 800 μm, more preferably 0.5 to 400 μm.

[0225] Furthermore, the windshield 24 has an adhesive layer 38 provided between the linear polarizing reflective film 10 and the second glass plate 30, and the linear polarizing reflective film 10 and the first glass plate 28 are bonded together using an interlayer film 36. However, the windshield 24 is not limited thereto. Specifically, an adhesive layer may be provided between the linear polarizing reflective film 10 and the first glass plate 28, and an interlayer film may be provided between the linear polarizing reflective film 10 and the second glass plate 30.

[0226] Alternatively, the windshield 24 may have no intermediate film 36 and may use an adhesive layer 38 for bonding the linear polarizing reflective film 10 to the first glass plate 28 and the second glass plate 30 .

[0227] In the HUD 20 , the windshield 24 has the following structure: a reflective film 10 is provided between a first glass plate 28 and a second glass plate 30 , the linearly polarized light reflective film 10 being bonded to the second glass plate 30 via an adhesive layer 38 , and the linearly polarized light reflective film 10 being bonded to the first glass plate 28 via an intermediate film 36 .

[0228] like Figure 5 As shown, in the HUD 20 , a driver D who is an observer of the image observes a virtual image of a projection image formed by the projector 22 , which is projected by the projector 22 and reflected by the windshield 24 .

[0229] In a typical HUD, the projected image is reflected by the windshield, and the reflected light is observed. Typical windshields are made of laminated glass, consisting of two sheets of glass: an inner surface and an outer surface. Therefore, in a HUD, the driver experiences a double image due to the reflected light from the two sheets of glass.

[0230] To address this problem, in a typical HUD, the cross-sectional shape of the windshield (intermediate film) is made wedge-shaped so that the reflection from the inner surface side glass and the reflection from the outer surface side glass overlap, thereby preventing double images from being seen.

[0231] However, as described above, in a wedge-shaped windshield, when the imaging distance of the virtual image is changed to cope with the difference in the driver's line of sight between normal driving with a closer line of sight and high-speed driving with a farther line of sight, for example, the angle of the wedge shape of the windshield does not match, and the image observed by the driver becomes a double image.

[0232] In contrast, in the HUD 20 of the present invention, the projector 22 projects p-polarized light, and the windshield 24 includes a linearly polarized light reflective film 10 between the first glass plate 28 and the second glass plate 30 that reflects p-polarized light. The driver D observes the light reflected by the linearly polarized light reflective film 10. In this configuration, the reflection of the projected light from the projector 22 is primarily due to the reflection of the linearly polarized light reflective film 10, and thus ghosting is substantially less likely to occur.

[0233] Therefore, in the HUD 20 using the linearly polarized reflective film 10 of the present invention for the windshield 24 , it is not necessary to make the cross-sectional shape of the windshield 24 (intermediate film 36 ) wedge-shaped. Therefore, even if the formation distance of the virtual image is changed, ghosting does not occur.

[0234] The present invention is basically constructed as described above. While the linearly polarized light reflective film, windshield, and head-up display system (HUD) of the present invention have been described in detail above, the present invention is not limited to the aforementioned embodiments. Various improvements and modifications are possible without departing from the spirit of the present invention.

[0235] [Example]

[0236] Below, give embodiment and further specifically illustrate feature of the present invention.Within the scope that does not depart from the gist of the present invention, the material, reagent, amount of substance and its ratio and operation etc. shown in the following examples can suitably change.Therefore, the scope of the present invention is not limited to following embodiment.

[0237] [Example 1]

[0238] <Production of Linearly Polarized Light Reflective Film>

[0239] Based on the method described in Japanese Patent Application Publication No. 9-506837, a linearly polarized light reflecting film (selective reflecting layer) was produced as follows.

[0240] Using ethylene glycol as the diol, a copolyester of 2,6-polyethylene naphthalate (PEN) and naphthalene 70 / terephthalate 30 (coPEN) was synthesized in a standard polyester resin synthesis reactor. Monolayer films of PEN and coPEN were extruded, stretched at a draw ratio of 5:1 at approximately 150°C, and heat-treated at approximately 230°C for 30 seconds. The refractive index of PEN, relative to the slow axis (orientation axis), was approximately 1.86, and the refractive index relative to the transverse axis was 1.64. The refractive index of the coPEN film was also confirmed to be approximately 1.64.

[0241] Next, by adjusting the stretch ratio, we confirmed that the refractive index of the PEN film relative to the slow axis was approximately 1.71, and the refractive index relative to the horizontal axis was 1.64, resulting in a refractive index of approximately 1.64 for the coPEN film. This means that the difference Δn between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer was 0.07.

[0242] Next, PEN and coPEN were simultaneously extruded using a 25-slot feed block equipped with a standard extrusion die, thereby forming 16 layers of PEN and coPEN alternating with the film thicknesses shown in (1) of Table 1 below. Furthermore, by repeating the same operation, 16 layers of PEN and coPEN each having the thicknesses shown in (2) to (6) of Table 1 were alternately formed in sequence, thereby producing a laminated body having a total of 96 layers.

[0243] [Table 1]

[0244] Table 1

[0245]

[0246] Next, the stretched laminate was heat-treated in an air oven at approximately 230°C for 30 seconds to produce a linearly polarized light reflective film. The thickness of the produced linearly polarized light reflective film was approximately 10 μm. The reflectance spectrum of the linearly polarized light reflective film was measured using a spectrophotometer (V-670, manufactured by JASCO Corporation). The results showed a reflectance spectrum with reflectance peaks at reflection bands of 450 nm, 550 nm, 650 nm, 700 nm, 750 nm, and 800 nm.

[0247] [Examples 2 to 4, Comparative Examples 1 to 3]

[0248] The refractive index of the PEN layer in the slow axis direction, that is, the difference Δn between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer, and the film thickness and number of layers of the PEN layer (optically anisotropic layer) and the coPEN layer (slow axis direction) were appropriately changed to produce linearly polarized light reflective films having the reflection peaks shown in Table 2 below.

[0249] The wavelength, reflectivity, wavelength band, and presence or absence of contact of the light-reflecting layers of the reflection peaks of each Example and Comparative Example are shown in Table 2. In Table 2, when there are multiple third reflection peaks, each reflection peak is classified as third A, third B, third C, and third D.

[0250] In Examples 1 to 3, the intensity ratios of the first, second, and third reflection peaks were all between 80% and 120%. In Example 4, the intensity ratios of the first and second reflection peaks were 150%, and the intensity ratios of the first and third reflection peaks were 125%.

[0251] In addition, the reflectivity and wavelength bandwidth in each reflection peak in each Example and Comparative Example were measured as follows.

[0252] The prepared linearly polarized light reflecting film was attached to the surface of a glass plate, and a black PET film (light absorber) was attached to the back surface of the glass plate.

[0253] Using a spectrophotometer (V-670 manufactured by JASCO Corporation), P-polarized light and S-polarized light were incident on the surface of the linearly polarized reflective film at an angle of 5° relative to the normal direction, and the reflectance spectra from 400 nm to 1000 nm were measured. The average value of the measured P-polarized light reflectance spectra and S-polarized light reflectance spectra (average reflectance spectrum) was calculated.

[0254] Furthermore, the reflectivity for incident P-polarized light is synonymous with the average of the reflectivity for incident S-polarized light and the reflectivity for incident unpolarized light (natural light). In other words, the reflectivity spectrum for P-polarized light is synonymous with the average of the reflectivity spectrum for incident S-polarized light and the reflectivity spectrum for incident natural light.

[0255] According to the calculated average value of the reflection spectra of P-polarized light and S-polarized light,

[0256] Extract the reflection peak (maximum) in the wavelength band of 430nm to 500nm as the first reflection peak, and calculate its reflectivity and wavelength bandwidth.

[0257] Extract the reflection peak (maximum) in the wavelength band of 530nm to 600nm as the second reflection peak, and calculate its reflectivity and wavelength bandwidth.

[0258] Reflection peaks (maximum values) in the wavelength band of 600 nm to 800 nm were extracted as third reflection peaks, and the number of peaks, reflectivity, and wavelength bandwidth were calculated.

[0259] The wavelength bandwidth of the first reflection peak is the width of a region where the reflectance is higher than the average value of the maximum and minimum reflectances in the wavelength band of 430 nm to 500 nm.

[0260] The wavelength bandwidth of the second reflection peak is the width of a region where the reflectance is higher than the average value of the maximum and minimum reflectances in the wavelength band of 530 nm to 600 nm.

[0261] The wavelength bandwidth of the third reflection peak is the width of a region where the reflectance is higher than the average value of the maximum and minimum reflectances in the wavelength band of 600 nm to 800 nm.

[0262] In Comparative Example 2, the first reflection peak and the second reflection peak overlap, and the wavelength bandwidth extends from the wavelength region of 430 nm to 500 nm to the wavelength region of 530 nm to 600 nm.

[0263] [Table 2]

[0264] Table 2

[0265]

[0266] <Windshield Production>

[0267] Windshields having each of the linearly polarized light reflecting films produced above were produced as follows.

[0268] A glass plate (manufactured by Central Glass Co., Ltd., FL2, visible light transmittance 90%) having a length of 120 mm and a width of 100 mm and a thickness of 2 mm was prepared.

[0269] A PVB film having a thickness of 0.38 mm, manufactured by Sekisui Chemical Co., Ltd., was placed on the glass plate. A linearly polarized light reflective film cut into a sheet having dimensions of 110 mm long by 90 mm wide was placed on the interlayer film with the slow axis aligned with the longitudinal direction.

[0270] A glass plate (manufactured by Central Glass Co., Ltd., FL2, visible light transmittance 90%) having a length of 120 mm and a width of 100 mm and a thickness of 2 mm was placed on the linear polarized light reflecting film.

[0271] The laminate was maintained at 90°C and 10 kPa (0.1 atm) for one hour and then heated in an autoclave (manufactured by Kurihara Seisakusho) at 115°C and 1.3 MPa (13 atm) for 20 minutes to remove bubbles, thereby obtaining a windshield.

[0272] [Evaluation of visible light transmittance]

[0273] The transmittance spectrum was measured using a spectrophotometer (V-670, manufactured by JASCO Corporation) with natural light incident from the opposite side of the glass in contact with the film at a 0° angle relative to the normal direction of the glass. In accordance with JIS R3106, the transmittance was calculated by multiplying the transmittance by the coefficient corresponding to the visual sensitivity and the emission spectrum of light source A for each 10 nm wavelength between 380 and 780 nm. Transmittance was evaluated according to the following criteria.

[0274] Transmittance evaluation criteria

[0275] A: 80% or more (when laminated glass is made of green glass, the transmittance is 70% or more)

[0276] B: Less than 80% (In the case of laminated glass made of green glass, the transmittance is less than 70%. This does not meet legal requirements.)

[0277] [Evaluation of P-polarized light reflectivity]

[0278] P-polarized light was incident from the glass side in contact with the film at an angle of 65° relative to the normal direction of the glass. The reflectance spectrum of the specularly reflected light (the direction of 65° relative to the normal direction on the opposite side of the incident plane relative to the normal direction) was measured using a spectrophotometer (V-670 manufactured by JASCO Corporation). The longitudinal direction (longitudinal direction) of the linearly polarized light reflective film was aligned with the transmission axis of the incident P-polarized light in the spectrophotometer.

[0279] According to JIS R3106, the reflectance of the projected image is calculated by multiplying the reflectance by the coefficient corresponding to the visual sensitivity and the emission spectrum of the D65 light source at every 10 nm wavelength between 380 and 780 nm. This is then evaluated as brightness. Brightness is evaluated according to the following criteria.

[0280] Evaluation criteria for P-polarized light reflectivity

[0281] A: 25% or more (the image can be seen in the P-polarized light reflection system of the HUD, and ghosting is difficult to see)

[0282] B: 20% or more to less than 25% (In the P-polarized light reflection system of the HUD, the image can be seen, but ghosting is visible.)

[0283] C: Less than 20% (The image is difficult to see clearly in the HUD's P-polarized light reflection system, and ghosting is well visible.)

[0284] [Evaluation of reflection color]

[0285] The reflectance at incident angles of 5° and 60° in natural light was measured in the same manner as for the transmittance, and the reflected color a* and b* were calculated from the spectrum.

[0286] Evaluation criteria for reflective color

[0287] AA: |a*|≤3, and |b*|≤3 (appears white when projecting white)

[0288] A: |a*|≤5, and |b*|≤5 (except for AA) (when projecting white, it looks roughly white)

[0289] B: Either a* or b* is larger

[0290] |a*|≤7, and |b*|≤7 (except for AA or A) (appears very slightly tinted when projecting white)

[0291] C: Either a* or b* is larger

[0292] |a*|≤9, and |b*|≤9 (except for AA, A, or B) (appears slightly tinted when projecting white)

[0293] D: a* and b* are both large

[0294] 9<|a*|, or 9<|b*| (when projecting white, it looks like another color)

[0295] The results are shown in Table 3.

[0296] [Table 3]

[0297] Table 3

[0298]

[0299] As shown in Table 3, it can be seen that the Examples obtained better results in terms of transmittance, P-polarized light reflectance (brightness), and reflected color than the Comparative Examples.

[0300] From the comparison of Examples 1 to 3, it can be seen that the difference Δn between the refractive index in the slow axis direction of the optically anisotropic layer and the refractive index of the isotropic layer is preferably 0.05 to 0.14, more preferably 0.05 to 0.10.

[0301] Furthermore, as can be seen from the comparison between Example 1 and Example 4, the intensity ratio of each reflection peak is preferably 80% or more and 120% or less.

[0302] The above results clearly demonstrate the effects of the present invention.

[0303] [Industrial Applicability]

[0304] The present invention can be suitably used in a vehicle-mounted head-up display system (HUD) or the like.

[0305] Explanation of symbols

[0306] 10 Linear polarized light reflective film

[0307] 11 First stacking section

[0308] 11a, 12a, 13a Optically anisotropic layers

[0309] 11b, 12b, 13b Isotropic layers

[0310] 12 Second laminated portion

[0311] 13 Third stacking section

[0312] 20 Head-up display system (HUD)

[0313] 22 Projector

[0314] 24 Windshield

[0315] 25, 30a surface

[0316] 28 First Glass Plate

[0317] 30 Second Glass Plate

[0318] 36 Intermediate film

[0319] 38 adhesive layer

[0320] D Driver

[0321] H-axis

[0322] Y up and down direction

Claims

1. A linearly polarized light reflecting film comprising a selective reflecting layer formed by laminating an optically anisotropic layer and an isotropic layer, The difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is 0.03 to 0.2, The selective reflection layer satisfies all of the following items: Item (i) has at least one first reflection peak with a central reflection wavelength of 430 nm or more and less than 500 nm, and the natural light reflectivity at the first reflection peak is 10% or more and 20% or less; Item (ii) has at least one second reflection peak with a central reflection wavelength of 530 nm or more and less than 600 nm, and the natural light reflectivity at the second reflection peak is 10% or more and 20% or less; Item (iii) has a third reflection peak with a central reflection wavelength of 600 nm to 800 nm, and the third reflection peak satisfies any of the following conditions: (a) having two or more reflection peaks and a natural light reflectivity of not less than 10% and not more than 20%; (b) There is one reflection peak, the natural light reflectance is 10% to 20%, and the wavelength bandwidth of the region where the reflectance is higher than the average of the maximum and minimum reflectances at 600 nm to 800 nm is 120 nm or more.

2. The linearly polarized light reflective film according to claim 1, wherein The third reflection peak of the item (iii) of the selective reflection layer satisfies only the item (a).

3. The linearly polarized light reflective film according to claim 1 or 2, wherein: The intensity ratio of the first reflection peak to the second reflection peak is greater than or equal to 80% and less than or equal to 120%. The intensity ratio of the first reflection peak to the third reflection peak is greater than or equal to 80% and less than or equal to 120%. An intensity ratio of the second reflection peak to the third reflection peak is greater than or equal to 80% and less than or equal to 120%.

4. The linearly polarized light reflective film according to claim 1 or 2, wherein: The wavelength bandwidth of the region where the reflectivity is higher than the average of the maximum and minimum values of the reflectivity of the first reflectivity peak at 430 nm to 500 nm is 20 nm to 95 nm. The wavelength bandwidth of the region where the reflectance is higher than the average value of the maximum and minimum values of the reflectance at the second reflectance peak at 530 nm to 600 nm is 20 nm to 95 nm.

5. The linearly polarized light reflective film according to claim 1 or 2, wherein: The selective reflection layer is composed of two or more light reflection layers that selectively reflect different wavelengths. The light reflecting layers having any one of the first reflection peak, the second reflection peak, and the third reflection peak are in contact with each other.

6. The linearly polarized light reflective film according to claim 1 or 2, wherein: The difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is 0.05 to 0.

14.

7. The linearly polarized light reflective film according to claim 1 or 2, wherein: The difference between the refractive index of the optically anisotropic layer in the slow axis direction and the refractive index of the isotropic layer is 0.05 to 0.

10. 8 . A windshield comprising the linearly polarized light reflecting film according to claim 1 between a first glass plate and a second glass plate. 9 . A head-up display system comprising the windshield according to claim 8 and a projector for irradiating p-polarized light projection image light toward the windshield.

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