Reflective film and head-up display system

Abstract

The present invention provides: a reflective film that, when applied as the combiner in a head-up display system, can realize a head-up display system that exhibits an excellent luminance when viewed from the front direction and an excellent luminance when viewed in an oblique direction; and a head-up display system. The reflective film according to the present invention comprises: a linearly polarized reflective layer containing an optically anisotropic layer and an isotropic layer; and a polarization conversion layer. The polarization conversion layer satisfies prescribed requirements, and the width of the reflective film in the direction orthogonal to the in-plane slow axis of the optically anisotropic layer is at least 300 mm.

Description

Reflective film, head-up display system

[0001] The present invention relates to a reflective film and a head-up display system.

[0002] In recent years, various types of head-up displays have been widely applied in our daily lives, and in particular, head-up displays that display information by superimposing an image on an environmental image are commonly used in vehicles and aircraft, etc. Taking vehicle head-up displays as an example, a reflective film is used as a combiner to provide information to the driver, allowing the driver to check the information provided by the in-vehicle information system while driving without having to look down to see the display board or navigation system.

[0003] Patent Document 1 discloses a linearly polarized light reflective film that can be applied to a head-up display.

[0004] International Publication No. 2021 / 200652

[0005] In recent years, in head-up display systems, efforts have been made to widen the horizontal width of the reflective film that functions as a combiner in order to project more images. On the other hand, from the perspective of image visibility, excellent brightness is required both when the reflective film is viewed from a fixed position, such as the driver's seat of a vehicle, facing forward and when the reflective film is viewed from an oblique direction. The present inventors fabricated a wide reflective film using a conventional linearly polarized reflective film such as that described in Patent Document 1, applied it to a head-up display system, and examined its functionality. However, they found that the brightness characteristics described above could not be obtained. In particular, the brightness was significantly reduced when the reflective film was viewed from a fixed position, such as the driver's seat, facing obliquely.

[0006] In view of the above circumstances, an object of the present invention is to provide a reflective film that, when used as a combiner in a head-up display system, can realize a head-up display system that is excellent in both luminance when viewed from the front and luminance when viewed from an oblique direction. Another object of the present invention is to provide a head-up display system.

[0007] The present inventors have found that the above problems can be solved by the following configuration.

[0008] (1) A reflective film having a linearly polarized light reflective layer including an optically anisotropic layer and an isotropic layer, and a polarization conversion layer, wherein the polarization conversion layer satisfies the requirement (A) or (B) described below, and the width of the reflective film in a direction perpendicular to the in-plane slow axis of the optically anisotropic layer is 300 mm or more. (2) The reflective film according to (1), wherein the polarization conversion layer satisfies the requirement (A), the retardation layer has an in-plane retardation of 100 to 500 nm at a wavelength of 550 nm, and the angle formed between the molecular axis of the liquid crystal compound located at one end in one direction and the molecular axis of the liquid crystal compound located at the other end in the same direction is 3 to 40°. (3) The reflective film according to (1) or (2), wherein the polarization conversion layer satisfies requirement (A), the retardation layer has an in-plane retardation of 210 to 340 nm at a wavelength of 550 nm, and the angle formed between the molecular axis of the liquid crystal compound located at one end in one direction and the molecular axis of the liquid crystal compound located at the other end in the same direction is 7 to 15°. (4) The reflective film according to (1), wherein the polarization conversion layer satisfies requirement (B), and the pitch number x of the helical orientation structure and the film thickness y (μm) of the polarization conversion layer satisfy the relationships of the below-described formulas (3) and (4). (5) A head-up display system comprising the reflective film according to any one of (1) to (4) and a projector that irradiates projection light onto the reflective film. (6) The head-up display system according to (5), wherein the projector emits P-polarized light as projection light.

[0009] According to the present invention, it is possible to provide a reflective film that, when applied as a combiner in a head-up display system, can realize a head-up display system that is excellent in both luminance when viewed from the front and luminance when viewed from an oblique direction. Also, according to the present invention, it is possible to provide a head-up display system.

[0010] 1 is a schematic diagram of a conventional head-up display system as viewed from the side. FIG. 1 is a schematic diagram of the head-up display system of FIG. 1 as viewed from above. FIG. 1 is a schematic diagram of the head-up display system of the present invention as viewed from the side. FIG. 2 is a schematic diagram of the head-up display system of FIG. 2 as viewed from above. FIG. 12 is a schematic diagram showing an example of a linearly polarized light reflective layer. FIG. 5 is a schematic diagram of the linearly polarized light reflective layer as viewed from the normal direction. FIG. 13 is a diagram showing the orientation (direction) of the molecular axis of a liquid crystal compound in a retardation layer. FIG. 14 is a diagram for explaining an exposure method for a photo-alignment film. FIG. 15 is a diagram for explaining a polarizer used. FIG. 16 is a schematic diagram of the head-up display system used in Examples and Comparative Examples as viewed from the side. FIG. 17 is a schematic diagram of the head-up display system of FIG. 12 as viewed from above.

[0011] The reflective film and head-up display system of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. Note that the drawings described below are merely illustrative for explaining the present invention, and the present invention is not limited to the drawings shown below. Note that the "to" symbol indicating a numerical range below includes the values ​​written on both sides. For example, when ε1 is between the numerical value α1 and the numerical value β1, the range of ε1 includes the numerical values ​​α1 and β1, and expressed in mathematical notation, α1≦ε1≦β1.

[0012] 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.

[0013] The in-plane retardation (in-plane phase difference) is a value measured using an AxoScan manufactured by Axometrics. Unless otherwise specified, the measurement wavelength is 550 nm. The in-plane retardation is a value measured by irradiating light with a wavelength within the visible light wavelength range in the normal direction of the film.

[0014] A feature of the present invention is the use of a predetermined polarization conversion layer, as described below. First, problems with head-up display systems including a conventional reflective film using a linearly polarized light reflective layer will be described with reference to FIG. 1 . FIG. 1 is a schematic diagram of a head-up display system 100 observed from the side. The head-up display system 100 includes a projector 112 that emits projection light and a reflective film 114 onto which the projection light is incident. The reflective film 114 includes a substrate 116 and a linearly polarized light reflective layer 118. In the head-up display system 100 illustrated in FIG. 1 , the projection light emitted from the projector 112 is reflected by the reflective film 114 and observed by an observer OB, as indicated by the solid line. FIG. 2 is a schematic diagram of the head-up display system 100 shown in FIG. 1 observed from above, showing the optical path of the projection light emitted from the projector 112 and reaching the observer OB. As shown in FIG. 2 , when a wide reflective film 114 is used as a combiner, the projection light emitted from the projector 112 reaches the observer OB via various optical paths. The reflection axis of the linearly polarized light reflective layer 118 included in the reflective film 114 is parallel to the vertical direction (the up-down direction on the paper), as indicated by the arrow in FIG. 2 . For such a reflective film 114, linearly polarized light parallel to the reflection axis of the linearly polarized light reflective layer 118 emitted from the projector 112 from a position directly in front of the observer OB, as indicated by the black arrow, is reflected by the reflective film 114 and reaches the observer OB. Therefore, the observer can see a bright image projected on the reflective film 114 located directly in front of them. In contrast, with a wide reflective film 114, linearly polarized light is emitted from the projector 112 from a position horizontally away from the observer and reflected toward the observer OB, as indicated by the white arrow. When linearly polarized light parallel to the reflection axis of the linearly polarized light reflective layer 118 is emitted from an oblique direction onto such a reflective film 114, a change in polarization occurs in the film thickness direction of the linearly polarized light reflective layer 118 in the reflective film 114, and the reflectance of the linearly polarized light reflective layer 118 decreases.Therefore, when the observer OB views the image projected onto the reflective film 114 located diagonally from his / her own position (in Figure 2, to the left of the paper from the observer OB), the image is difficult to see because of its inferior brightness compared to an image projected in the front direction.

[0015] In response to the above-mentioned problems, the present invention provides a head-up display system that is excellent in both the brightness of an image projected in the direction directly in front of the observer and the brightness of an image projected in an oblique direction from the observer, by providing a predetermined polarization conversion layer on a linearly polarized light reflective layer. In particular, the polarization conversion layer described below changes the polarization direction of linearly polarized light when it is emitted to the reflective film from an oblique direction, as shown by the white arrow in Figure 2, as the linearly polarized light passes through the polarization conversion layer, and polarized light that takes into account the polarization change caused by the linearly polarized light reflective layer is irradiated onto the reflective film, thereby preventing a decrease in the reflection efficiency of the linearly polarized light reflective layer.

[0016] FIG. 3 shows an example of a head-up display system of the present invention. FIG. 3 is a schematic diagram of a head-up display system 10 observed from the side. The head-up display system 10 includes a projector 12 that emits projection light and a reflective film 14 onto which the projection light is irradiated. The reflective film 14 includes a substrate 16, a linearly polarized light reflective layer 18, and a polarization conversion layer 20. In the head-up display system 10 illustrated in FIG. 3, the projection light emitted from the projector 12 is reflected by the reflective film 14 and observed by an observer OB, as indicated by the solid line. FIG. 4 is a schematic diagram of the head-up display system 10 shown in FIG. 3 observed from above, showing the optical path of the projection light emitted from the projector 12 that reaches the observer OB. As described above, in the head-up display system 10, both the projection light emitted from the projector 12 from a position directly in front of the observer OB, as indicated by the black arrow, and the projection light emitted from the projector 12 in an oblique direction toward the wide reflective film 14, as indicated by the white arrow, reach the observer efficiently, and therefore the brightness is excellent both when the observer OB views the reflective film 14 in a directly in front direction and when the observer views the reflective film 14 in an oblique direction.

[0017] The reflection axis in the linearly polarized reflective layer 18 included in the reflective film 14 is parallel to the vertical direction in FIG. 4 (the up-down direction on the paper surface in FIG. 4). As will be described later, the linearly polarized reflective layer 18 is a layer formed by laminating an optically anisotropic layer and an isotropic layer, and the direction of the reflection axis of the linearly polarized reflective layer 18 corresponds to the direction of the in-plane slow axis of the optically anisotropic layer. In other words, the direction of the in-plane slow axis of the optically anisotropic layer in FIG. 4 corresponds to the direction of the arrow shown in the reflective film 14 in FIG. 4. In the reflective film 14, the width W (length) of the reflective film 14 in the direction perpendicular to the in-plane slow axis of the optically anisotropic layer (which also corresponds to the direction perpendicular to the reflection axis in the linearly polarized reflective layer 18) is 300 mm or more. The width (length) is preferably 300 to 1500 mm, more preferably 400 to 1200 mm. The width W of the reflective film 14 also corresponds to the width (length) of the reflective film 14 in a direction perpendicular to the vertical direction when the reflective film 14 is applied to a head-up display system 10. The length of the reflective film 14 in a direction perpendicular to the width W (which also corresponds to the length in a direction parallel to the in-plane slow axis of the optically anisotropic layer) is not particularly limited, but is often equal to or less than the width W, and more often smaller than the width W. In particular, the ratio of the length of the reflective film in a direction perpendicular to the in-plane slow axis of the optically anisotropic layer (corresponding to the width W) to the length of the reflective film in a direction parallel to the in-plane slow axis of the optically anisotropic layer is preferably 1.0 to 25, more preferably 1.5 to 12, and even more preferably 2.0 to 7.5. In the present invention, the shape of the reflective film is not particularly limited as long as it satisfies the above width requirement, but is often rectangular.

[0018] Each component of the head-up display system 10 will be described in detail below.

[0019] <Projector> The configuration of the projector 12 is not particularly limited as long as it can emit projection light to the reflective film 14, and any known projector can be used.

[0020] The projection light emitted by the projector 12 is preferably P-polarized light. The projector 12 may have a polarizer therein in order to emit P-polarized projection light.

[0021] Examples of the projector 12 include an LCOS (Liquid Crystal on Silicon) projector, a laser projector, and a liquid crystal projector (liquid crystal display device).

[0022] <Substrate> The reflective film 14 includes a substrate 16. In the reflective film of the present invention, the substrate is an optional component and does not necessarily need to be included in the reflective film. The substrate 16 is a component that supports the linearly polarized light reflective layer 18 and the polarization conversion layer 20. The material of the substrate 16 is not particularly limited, and examples thereof include resin and glass. When the substrate 16 is a resin substrate, examples of the substrate 16 include plastic films such as polyesters such as polyethylene terephthalate (PET), polycarbonates, acrylic resins, epoxy resins, polyurethanes, polyamides, polyolefins, cellulose derivatives, and silicones.

[0023] The thickness of the substrate 16 may be about 5.0 to 1000 μm, preferably 10 to 250 μm, and more preferably 15 to 90 μm.

[0024] <Linearly Polarized Reflective Layer> The reflective film 14 includes a linearly polarized reflective layer 18. Fig. 5 is a schematic diagram showing an example of the linearly polarized reflective layer 18. Fig. 6 is a schematic diagram showing the linearly polarized reflective layer 18 as viewed from the normal direction. As shown in Fig. 5, the linearly polarized reflective layer 18 is formed by alternately laminating optically anisotropic layers 18a and isotropic layers 18b. In the linearly polarized reflective layer 18, the refractive index n ｅ１ is the refractive index n of the isotropic layer 18b ｏ２ and the refractive index n ｏ１ is the refractive index n of the isotropic layer 18b ｏ２The optically anisotropic layers 18a are laminated so that their in-plane slow axes are parallel to each other. Therefore, as shown in FIG. 6, in one direction (the vertical direction in FIG. 6), the refractive index (n ｅ１ ) and a layer with a high refractive index (n ｏ２ On the other hand, in the direction perpendicular to this direction (the left-right direction in FIG. 6), layers with the same refractive index are stacked.

[0025] 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 layer 18 shown in Figures 5 and 6 reflects linearly polarized light in the in-plane slow axis direction of the optically anisotropic layer 18a (the up-down direction in Figure 6) and transmits linearly polarized light in the left-right direction.

[0026] That is, the linearly polarized reflective layer 18 is a layer that selectively reflects linearly polarized light in a specific wavelength range. The linearly polarized reflective layer 18 preferably exhibits selective reflection in a portion of the visible light wavelength range. The linearly polarized reflective layer 18 may, for example, reflect light for displaying a projected image. The reflective film 14 may be configured to have a plurality of linearly polarized reflective layers 18 corresponding to each wavelength range. The linearly polarized reflective layer 18 can transmit linearly polarized light that is not reflected. Therefore, by having the linearly polarized reflective layer 18, the reflective film 14 can transmit a portion of light even in the wavelength range in which the linearly polarized reflective layer 18 exhibits reflection.

[0027] In a linearly polarized light reflective layer in which low-refractive index layers and high-refractive index layers are stacked, the reflected wavelength and reflectance can be adjusted by the refractive index difference between the low-refractive index layers and the high-refractive index layers, the thickness, the number of layers, etc. Specifically, the wavelength λ of reflected light can be adjusted by setting the thickness d of the low-refractive index layers and the high-refractive index layers to d = λ / (4 x n) where λ is the wavelength of reflected light and n is the refractive index. Furthermore, since the reflectance increases with the number of low-refractive index layers and high-refractive index layers stacked, the reflectance can be adjusted by adjusting the number of layers stacked. Furthermore, the width of the reflection band can be adjusted by the refractive index difference between the low-refractive index layers and the high-refractive index layers.

[0028] Materials and methods for preparing the linearly polarized light reflective layer can be those described, for example, in JP-A-9-506837. Specifically, a wide variety of materials can be used to form the linearly polarized light 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.

[0029] A commercially available product can be used as the linearly polarized reflective layer. A commercially available product that is a laminate of a reflective polarizing plate and a temporary support can be used. Examples of commercially available products include commercially available optical films sold under the names PICASUS (registered trademark) (manufactured by Toray Industries, Inc.), DBEF (registered trademark) (manufactured by 3M Corporation), and APF (Advanced Polarizing Film (manufactured by 3M Corporation)). The thickness of the linearly polarized reflective layer is preferably 2.0 to 50 μm, more preferably 8.0 to 30 μm. The number of laminations of optically anisotropic layers and isotropic layers in the linearly polarized reflective layer may be appropriately set depending on the required reflectivity, etc., but is preferably 10 to 200 layers.

[0030] <Polarization conversion layer> The reflective film 14 includes a polarization conversion layer 20. The polarization conversion layer 20 satisfies the following requirement (A) or (B): (A) The polarization conversion layer is a retardation layer, and the retardation layer contains a liquid crystal compound, and the orientation of the molecular axis of the liquid crystal compound changes continuously or stepwise along one direction in the plane of the retardation layer. (B) The polarization conversion layer is a layer in which a helical orientation structure of a liquid crystal compound is fixed, the liquid crystal compound being twisted and oriented along a helical axis extending along the thickness direction, and satisfies the relationships of formulas (1) and (2), where x is the pitch number of the helical orientation structure and y (μm) is the film thickness of the polarization conversion layer. Formula (1) 0.010≦x<0.100 Formula (2) 0.5≦y≦5.0 Requirements (A) and (B) are described in detail below.

[0031] (Requirement (A)) In requirement (A), the polarization conversion layer is a retardation layer. The retardation layer contains a liquid crystal compound, and the orientation of the molecular axis of the liquid crystal compound changes continuously or stepwise along one direction in the plane of the retardation layer. Hereinafter, the retardation layer will be described with reference to the drawings. FIG. 7 shows a plan view of the retardation layer. As shown in FIG. 7, the retardation layer 30 contains a liquid crystal compound LC, and the orientation of a molecular axis 32 of the liquid crystal compound LC changes while continuously rotating clockwise in one direction indicated by arrow X. Although the orientation of the molecular axis 32 of the liquid crystal compound LC rotates clockwise in FIG. 7, the present invention is not limited to this embodiment and may also rotate counterclockwise. The molecular axis 32 of the liquid crystal compound LC is the axis along which the refractive index of the liquid crystal compound LC is highest. For example, when the liquid crystal compound LC is a rod-shaped liquid crystal compound, the molecular axis is aligned with the long axis direction of the rod shape. When the liquid crystal compound LC is a discotic liquid crystal compound, the molecular axis is aligned with the direction perpendicular to the thickness direction of the disc.

[0032] The liquid crystal compounds LC contained in the retardation layer 30 are aligned in the Y direction perpendicular to the direction of the arrow X, i.e., in the Y direction perpendicular to one direction in which the molecular axes 32 continuously rotate. In other words, among the liquid crystal compounds LC contained in the retardation layer 30, the angles formed by the directions of the molecular axes 32 and the direction of the arrow X are equal among the liquid crystal compounds LC aligned in the Y direction.

[0033] FIG. 7 shows an embodiment in which the molecular axis of the liquid crystal compound LC rotates (changes) continuously in the direction of the arrow X, but the present invention is not limited to this embodiment, and the molecular axis may rotate (change) stepwise.

[0034] The angle between the molecular axis of the liquid crystal compound located at one end of the retardation layer 30 in the arrow X direction and the molecular axis of the liquid crystal compound located at the other end of the retardation layer 30 in the arrow X direction is not particularly limited, but when the reflective film of the present invention is applied as a combiner of a head-up display system, the brightness when viewed in the front direction and the brightness when viewed in an oblique direction are superior (hereinafter simply referred to as "the effect of the present invention is superior"). In other words, the rotation angle along the X-axis direction from the position of the molecular axis of the liquid crystal compound located at one end in the arrow X direction to the position of the molecular axis of the liquid crystal compound located at the other end in the arrow X direction of the retardation layer 30 is preferably 3 to 40 °, more preferably 7 to 15 °.

[0035] The in-plane retardation of the retardation layer 30 at a wavelength of 550 nm is not particularly limited, but is preferably 100 to 500 nm, more preferably 210 to 340 nm, in terms of achieving better effects of the present invention.

[0036] As described above with reference to FIGS. 1 and 2 , without a polarization conversion layer, the brightness of the displayed image is reduced by light emitted from a position horizontally distant from the viewer. In contrast, when the retardation layer 30 shown in FIG. 7 is used as the polarization conversion layer 20 shown in FIG. 4 , the molecular axis 32 of the liquid crystal compound LC in the retardation layer 30 is changed, thereby adjusting the polarization direction of projected light emitted from a position horizontally distant from the viewer and making it easier for the light to be reflected by the linearly polarized light reflective layer 18. More specifically, when the left end of the retardation layer 30 shown in FIG. 7 is applied so that the left end of the polarization conversion layer 20 shown in FIG. 4 is positioned on the left side of the paper, the molecular axis of the liquid crystal compound LC in the retardation layer 30 located in front of the viewer is parallel to the vertical direction. In other words, the molecular axis of the liquid crystal compound LC in the retardation layer 30 located in front of the viewer is parallel to the reflection axis of the linearly polarized light reflective layer 18. Therefore, even if linearly polarized light parallel to the reflection axis of the linearly polarized light reflective layer 18 is incident, the retardation layer 30 does not affect the linearly polarized light. On the other hand, the more the projection light is emitted from a position farther away from the viewer in the horizontal direction (see the white arrow in FIG. 4 ), the greater the change in polarization caused by the linearly polarized light reflective layer 18. Therefore, the polarization direction of the projection light irradiated onto the linearly polarized light reflective layer 18 is adjusted by tilting the direction of the molecular axis 32 of the liquid crystal compound LC in the retardation layer 30 more as the position is farther away from the viewer in the horizontal direction than the molecular axis of the liquid crystal compound LC located in front of the viewer.

[0037] The direction of the in-plane slow axis of the retardation layer is appropriately adjusted so as to obtain the effects of the present invention, but the angle between the one direction in which the orientation of the molecular axis of the liquid crystal compound changes and the reflection axis of the linearly polarized light reflective layer 18 is preferably 80 to 100°, more preferably 85 to 95°, and even more preferably 90°. In other words, the angle between the one direction and the in-plane slow axis of the optically anisotropic layer in the linearly polarized light reflective layer is preferably 80 to 100°, more preferably 85 to 95°, and even more preferably 90°. In the above embodiment, the molecular axis of the liquid crystal compound located at one end of the retardation layer in the one direction in which the orientation of the molecular axis of the liquid crystal compound changes is preferably parallel to the reflection axis of the linearly polarized light reflective layer. Furthermore, as described above, the rotation direction from the molecular axis of the liquid crystal compound located at one end of the retardation layer to the molecular axis of the liquid crystal compound located at the other end in the one direction in which the orientation of the molecular axis of the liquid crystal compound changes may be clockwise or counterclockwise. For example, when the reflective film is used as a combiner in a head-up display system of a vehicle in which the driver's seat is located on the left side, it is preferable that the molecular axis of the liquid crystal compound in the retardation layer rotates clockwise in the direction from the driver's seat to the passenger seat (from the left side to the right side of the paper in Fig. 7) as shown in Fig. 7. Furthermore, when the reflective film is used as a combiner in a head-up display system of a vehicle in which the driver's seat is located on the right side, it is preferable that the molecular axis of the liquid crystal compound in the retardation layer rotates counterclockwise in the direction from the driver's seat to the passenger seat.

[0038] As described above, the orientation of the molecular axis of the liquid crystal compound is rotated along one direction in the retardation layer, and the degree of rotation of the orientation of the molecular axis of the liquid crystal compound in the one direction is preferably 0.05 to 0.6° / cm, more preferably 0.1 to 0.5° / cm. The unit represents the rotation angle of the molecular axis of the liquid crystal compound per 1 cm in the one direction.

[0039] The thickness of the retardation layer is not particularly limited, and is preferably adjusted so as to fall within the above-mentioned range of in-plane retardation, preferably 0.6 to 3.0 μm, more preferably 1.2 to 2.0 μm.

[0040] The retardation layer contains a liquid crystal compound LC. As the liquid crystal compound, either a polymer liquid crystal compound or a low molecular weight liquid crystal compound can be used. Here, the term "polymer liquid crystal compound" refers to a liquid crystal compound having a repeating unit in its chemical structure. The term "low molecular weight liquid crystal compound" refers to a liquid crystal compound having no repeating unit in its chemical structure. The liquid crystal compound may be either a rod-shaped liquid crystal compound or a discotic liquid crystal compound, but a rod-shaped liquid crystal compound is preferred.

[0041] The liquid crystal compound in the retardation layer may be fixed. In this specification, the "fixed" state preferably refers to a state in which the alignment of the liquid crystal compound is maintained. Specifically, it is preferable that the layer has no fluidity and can stably maintain the fixed alignment state without causing changes in the alignment state due to external fields or external forces, usually at a temperature range of 0 to 50°C, or under more severe conditions, at a temperature range of -30 to 70°C. In addition, the liquid crystal compound in the retardation layer may no longer exhibit liquid crystallinity. For example, when the retardation layer is formed using a polymerizable liquid crystal compound, the liquid crystal compound may be polymerized by a curing reaction and may no longer have liquid crystallinity.

[0042] The retardation layer is preferably a layer formed using a composition containing a polymerizable liquid crystal compound. The polymerizable liquid crystal compound is a liquid crystal compound having a polymerizable group. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group. An unsaturated polymerizable group is preferred, and an ethylenically unsaturated polymerizable group is more preferred.

[0043] The method for manufacturing the retardation layer is not particularly limited, and known methods can be used. For example, a method including a step of forming a coating film by applying a retardation layer-forming composition containing a liquid crystal compound onto an alignment film (hereinafter also referred to as a "coating film forming step") and a step of orienting the liquid crystal compound contained in the coating film (hereinafter also referred to as an "orientation step") in this order is preferred. Each step will be described below.

[0044] The coating film forming step is a step of forming a coating film by applying a retardation layer forming composition onto an alignment film. The retardation layer forming composition contains a liquid crystal compound. As described above, the liquid crystal compound may be a polymerizable liquid crystal compound. The retardation layer forming composition may contain components other than the liquid crystal compound (e.g., a solvent, a polymerization initiator, etc.).

[0045] Examples of the method for applying the composition for forming the retardation layer include known methods such as roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, and inkjet.

[0046] The alignment film may be any film that aligns the liquid crystal compound that can be contained in the retardation layer-forming composition. It can be formed by means such as rubbing an organic compound (preferably a polymer) onto the film surface, oblique deposition of an inorganic compound, formation of a layer with microgrooves, or accumulation of an organic compound (e.g., ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearate) by the Langmuir-Blodgett method (LB film). Furthermore, alignment films that exhibit alignment function upon application of an electric field, application of a magnetic field, or light irradiation are also known. Among these, photo-alignment films formed by light irradiation are also preferred from the viewpoint of uniformity of alignment.

[0047] As the photo-alignment film, a photo-alignment film containing an azobenzene dye or polyvinyl cinnamate or the like is used.

[0048] Methods for imparting an orientation pattern to a photo-alignment film to align liquid crystal compounds include known exposure processes. Among these, a method of exposing a photo-alignment film using a combination of a mask having regions with different transmittances and a polarizer (e.g., a wire grid) (hereinafter, also referred to simply as a "specification method") is exemplified. An example of the specific method is described in detail below. To manufacture an alignment film having an orientation pattern capable of forming a liquid crystal layer with the molecular axes of liquid crystal compounds as shown in FIG. 7 using the specific method, two exposures are performed on the photo-alignment film. First, as shown in FIG. 8, a polarizer 42A and a mask 44A are placed on the photo-alignment film 40, and exposure is performed from the direction indicated by the white arrow. The transmission axis of the polarizer 42A is rotated counterclockwise by a predetermined angle relative to the front-to-back direction of the paper in FIG. 8. More specifically, FIG. 9 is a view of the polarizer 42A observed from the direction of the white arrow in FIG. 8, where the dashed arrow corresponds to the front-to-back direction of the paper in FIG. 8, and the solid arrow corresponds to the transmission axis of the polarizer 42A. Furthermore, the mask 44A has a transmittance that increases in the direction of the arrow shown in FIG. 8 . During the first exposure, the photo-alignment film 40 is irradiated with light along the transmission axis direction of the polarizer 42A. However, depending on the transmittance distribution of the mask 44A, stronger exposure is performed in the left region of the photo-alignment film 40 in FIG. 8 . Next, as shown in FIG. 10 , for the second exposure, a polarizer 42B and a mask 44B are placed on the photo-alignment film 40 that has been subjected to the first exposure, and exposure is performed from the direction indicated by the white arrow. The transmission axis of the polarizer 42B is positioned in a direction rotated a predetermined angle clockwise relative to the front-to-back direction of the paper in FIG. 10 . More specifically, FIG. 11 is a view of the polarizer 42B observed from the direction of the white arrow in FIG. 10 , where the dashed arrow corresponds to the front-to-back direction of the paper in FIG. 10 and the solid arrow corresponds to the transmission axis of the polarizer 42B. Furthermore, the mask 44B has a transmittance that increases in the direction of the arrow shown in Fig. 10. When the second exposure is performed, the photo-alignment film 40 is irradiated with light along the transmission axis direction of the polarizer 42B. However, in accordance with the transmittance distribution of the mask 44B, stronger exposure is performed in the right region of the photo-alignment film 40 in Fig. 10.In the above procedure, the transmittance distribution of the masks 44A and 44B and the positions of the polarizers 42A and 42B can be adjusted to adjust the magnitude of the function of aligning the liquid crystal compound at each position on the photo-alignment film 40. For example, in FIG. 9, the transmission axis of the polarizer 42A is positioned 10° counterclockwise from the dashed line, and in FIG. 11, the transmission axis of the polarizer 42B is positioned 10° clockwise from the dashed line. If the first and second exposure doses are the same, the effects of the two exposures cancel each other out, and the function of aligning the liquid crystal compound in the direction of the dashed line in FIG. 9 can be imparted. If the second exposure dose is increased, the function of aligning the liquid crystal compound along a direction tilted toward the transmission axis of the polarizer 42B can be imparted. Note that the direction in which the polarizer is arranged in the above-mentioned specific method is appropriately selected optimally depending on the material of the photo-alignment film used.

[0049] The alignment step is a step of aligning the liquid crystal compound contained in the coating film. The alignment step may include a drying treatment. The drying treatment can remove components such as a solvent from the coating film. The drying treatment may be performed by leaving the coating film at room temperature for a predetermined time (for example, natural drying), or by heating and / or blowing air.

[0050] The orientation step preferably includes a heat treatment. From the viewpoint of manufacturability, the heat treatment is preferably performed at a temperature of 10 to 250° C., more preferably 25 to 190° C. The heating time is preferably 1 to 300 seconds, more preferably 1 to 60 seconds.

[0051] The orientation step may include a cooling treatment carried out after the heating treatment. The cooling treatment is a treatment in which the coated film after heating is cooled to about room temperature (20 to 25°C). This further fixes the orientation of the liquid crystal compound contained in the coated film, thereby increasing the degree of orientation of the liquid crystal compound. The cooling method is not particularly limited and can be carried out by a known method.

[0052] After the alignment step, a step of curing the retardation layer (hereinafter also referred to as a "curing step") may be included. The curing step is performed, for example, by heating and / or light irradiation (exposure). Among these, the curing step is preferably performed by light irradiation. As the light source used for curing, various light sources such as infrared light, visible light, and ultraviolet light can be used, but ultraviolet light is preferred. Furthermore, ultraviolet light may be irradiated while heating during curing, or ultraviolet light may be irradiated through a filter that transmits only specific wavelengths. Furthermore, exposure may be performed under a nitrogen atmosphere.

[0053] (Requirement (B)) In requirement (B), the polarization conversion layer is a layer (hereinafter also referred to as a "twist layer") in which a helical orientation structure of a liquid crystal compound is fixed, the liquid crystal compound being twisted and oriented along a helical axis extending along the thickness direction. Furthermore, when the pitch number of the helical orientation structure is x and the film thickness of the polarization conversion layer (twist layer) is y (μm), the relationship between formulas (1) and (2) is satisfied. Formula (1) 0.010≦x<0.100 Formula (2) 0.5≦y≦5.0

[0054] The twist layer has an optical rotation function that rotates the direction of incident linearly polarized light. Therefore, by disposing the twist layer on the linearly polarized light reflective layer, the polarization direction of the projection light irradiated onto the linearly polarized light reflective layer 18 from a position horizontally away from the driver's seat can be adjusted, and the desired effect can be obtained, similar to the retardation layer.

[0055] As described above, the pitch number x of the helical orientation structure satisfies the relationship of formula (1), and preferably satisfies the relationship of formula (3). Formula (3) 0.014≦x≦0.050 Note that one pitch of the helical orientation structure of the liquid crystal compound is one turn of the helix of the liquid crystal compound. In other words, the pitch number 1 is defined as the state in which the director of the helically oriented liquid crystal compound (the long axis direction in the case of rod-shaped liquid crystal) rotates 360°. Furthermore, the film thickness y (μm) of the polarization conversion layer (twist layer) preferably satisfies the relationship of formula (2), and preferably satisfies the relationship of formula (4). Formula (4) 0.6≦y≦4.0

[0056] The liquid crystal compound contained in the twist layer may be the same as the liquid crystal compound contained in the retardation layer described above.

[0057] The liquid crystal compound in the twist layer is fixed. The liquid crystal compound in the twist layer may no longer exhibit liquid crystallinity. For example, when the twist layer is formed using a polymerizable liquid crystal compound, the liquid crystal compound may be polymerized by a curing reaction and may no longer exhibit liquid crystallinity.

[0058] The twist layer is preferably a layer formed using a composition containing a polymerizable liquid crystal compound. The polymerizable liquid crystal compound is a liquid crystal compound having a polymerizable group. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group. An unsaturated polymerizable group is preferred, and an ethylenically unsaturated polymerizable group is more preferred.

[0059] The method for producing the twist layer is not particularly limited, and known methods can be used. For example, a method including, in this order, a step of applying a composition for forming a twist layer containing a polymerizable liquid crystal compound and a chiral agent to form a coating film, a step of orienting the liquid crystal compound contained in the coating film, and a step of polymerizing and fixing the polymerizable liquid crystal compound in the coating film is preferred. Each step will be described below.

[0060] The chiral agent has the function of inducing a helical structure of the cholesteric liquid crystal phase. The chiral compound may be selected according to the purpose, since the sense or pitch of the helix induced varies depending on the compound. The chiral agent may have a polymerizable group. Examples of the chiral agent include isosorbide derivatives, isomannide derivatives, and binaphthyl derivatives. Commercially available isosorbide derivatives, such as LC756 manufactured by BASF, may also be used.

[0061] The method for applying the composition for forming a twist layer may be the same as the method for applying the composition for forming a retardation layer described above.

[0062] The step of orienting the liquid crystal compound contained in the applied coating film preferably includes a heat treatment. From the viewpoint of manufacturability, the heat treatment is preferably performed at a temperature of 10 to 250° C., more preferably 25 to 190° C. The heating time is preferably 1 to 300 seconds, more preferably 1 to 60 seconds.

[0063] The above process may include a cooling treatment carried out after the heating treatment. The cooling treatment is a treatment in which the coated film after heating is cooled to about room temperature (20 to 25°C). This further fixes the orientation of the liquid crystal compound contained in the coated film, thereby increasing the degree of orientation of the liquid crystal compound. The cooling method is not particularly limited and can be carried out by a known method.

[0064] After the above steps, a step of curing the coating film may be included. The curing step is carried out, for example, by heating and / or light irradiation (exposure). Among these, the curing step is preferably carried out by light irradiation. As the light source used for curing, various light sources such as infrared light, visible light, and ultraviolet light can be used, but ultraviolet light is preferred. Furthermore, ultraviolet light may be irradiated while heating during curing, or ultraviolet light may be irradiated through a filter that transmits only specific wavelengths. Furthermore, exposure may be carried out in a nitrogen atmosphere.

[0065] The reflective film may include other components in addition to the above-mentioned substrate, linearly polarized light reflective layer, and polarization conversion layer, such as a pressure-sensitive adhesive layer and an adhesive layer.

[0066] <Uses> The head-up display system of the present invention can be used in a variety of applications, including, for example, an in-vehicle head-up display system.

[0067] 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.

[0068] <Preparation of Linearly Polarized Reflective Film> A linearly polarized reflective film was prepared as follows, based on the method described in JP-A-9-506837. 2,6-polyethylene naphthalate (PEN) and a 70% naphthalate / 30% terephthalate copolyester (coPEN) were synthesized in a standard polyester resin synthesis reactor using ethylene glycol as the diol. Monolayer films of PEN and coPEN were extruded and stretched at approximately 150°C with adjusted longitudinal and transverse stretch ratios, and then heat-treated at approximately 230°C for 30 seconds. The refractive index of the PEN film along its in-plane slow axis (orientation axis) was confirmed to be approximately 1.74, the refractive index along the transverse axis was 1.64, and the refractive index of the coPEN film was confirmed to be approximately 1.64. That is, the difference Δn between the refractive index of the optically anisotropic layer along the in-plane slow axis and the refractive index of the isotropic layer was 0.10. Next, PEN and coPEN were co-extruded using a 25-slot feed block equipped with a standard extrusion die under conditions that satisfied the above-mentioned Δn relationship, thereby forming seven alternating layers of PEN and coPEN, each with a thickness shown in (1) of Table 1 below. The same procedure was then repeated to form PEN and coPEN layers with thicknesses shown in (2) to (6) of Table 1, alternately, in the number of layers shown in Table 1, thereby producing a laminate with a total of 92 layers. The stretched laminate was then heat-treated in an air oven at approximately 230°C for 30 seconds to produce a linearly polarized reflective film. The reflection spectrum of this linearly polarized reflective film was measured using a spectrophotometer (V-670, manufactured by JASCO Corporation), and a reflection spectrum with reflectance peaks at 470 nm, 500 nm, 550 nm, 600 nm, 650 nm, and 720 nm was obtained.

[0069]

[0070] <Preparation of Retardation Layer> A TAC (celluloacylate film) measuring 1000 mm wide x 200 mm long was prepared as a support. The following composition for forming an alignment film was applied to the support by spin coating. The support on which the coating film of the composition for forming an alignment film was formed was dried on a hot plate at 60°C for 60 seconds to form alignment film P-1.

[0071] --Composition for forming alignment film---------------------------------- 1.00 part by mass of the following photoalignment material; 16.00 parts by mass of water; 42.00 parts by mass of butoxyethanol; 42.00 parts by mass of propylene glycol monomethyl ether.

[0072] Material for photo alignment

[0073]

[0074] The obtained alignment film P-1 was subjected to light irradiation in a specific method of performing two exposures as described in FIGS. 8 to 11 . The transmission axis of the polarizer and the transmittance of the mask used were adjusted so as to obtain a retardation layer 1 exhibiting the characteristics described below. Specifically, the transmission axis of the polarizer (wire grid) in the first exposure was positioned at a position rotated a predetermined angle counterclockwise with respect to the direction of the arrow indicating the transmittance distribution of mask 44A, and ultraviolet light was irradiated in the first exposure. Furthermore, the transmission axis of the polarizer (wire grid) in the second exposure was positioned at a position rotated a predetermined angle clockwise with respect to the direction of the arrow indicating the transmittance distribution of mask 44B, and ultraviolet light was irradiated in the second exposure. The irradiation dose in the first and second exposures was appropriately adjusted so as to obtain a retardation layer 1 described below. Furthermore, the transmittance distribution of the masks used (mask 44A and mask 44B) was also appropriately adjusted so as to obtain a retardation layer 1 described below.

[0075] Next, the following components were mixed to prepare a retardation layer-forming composition having the following composition: 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 give a solute concentration of 20% by mass

[0076]

[0077]

[0078]

[0079] A composition for forming a retardation layer was dropped onto the alignment film P-1 that had been subjected to the exposure treatment obtained above, and spin-coated to a film thickness of about 1.5 μm, followed by drying to obtain a coating film of the composition for forming a retardation layer. Next, the support with the coating film obtained 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 ) was used to irradiate the coating with ultraviolet light for 6 seconds to fix the liquid crystal phase. As a result, a retardation layer 1 was obtained whose thickness was adjusted to achieve the desired in-plane retardation. The orientation of the molecular axis of the liquid crystal compound at one end of the lateral direction of the prepared retardation layer 1 was 90° with respect to the lateral direction of the retardation layer 1 (corresponding to the lateral direction of 1000 mm of the support) (corresponding to the molecular axis of the liquid crystal compound located at the left end of the paper in FIG. 7). Furthermore, the orientation of the molecular axis of the liquid crystal compound at the other end of the lateral direction of the prepared retardation layer 1 was 80° with respect to the lateral direction of the retardation layer 1 (corresponding to the lateral direction of 1000 mm of the support) (corresponding to the molecular axis of the liquid crystal compound located at the right end of the paper in FIG. 7). In addition, in the retardation layer 1, the orientation of the molecular axis of the liquid crystal compound continuously changed in the direction from one end (left end) of the retardation layer 1 to the other end (right end) (see FIG. 7). The orientation (azimuth angle) of the molecular axis of the liquid crystal compound is a value expressed under the condition that the azimuth angle increases in the counterclockwise direction, with the horizontal direction of the retardation layer 1 being 0°. In addition, the in-plane retardation was 276 nm at any position of the retardation layer 1, including the one end and the other end.

[0080] The retardation layer 2 was produced in the same manner as the retardation layer 1, except that the mask density, the transmission axis of the wire grid, and the thickness of the retardation layer were appropriately adjusted. The characteristics of each retardation layer are shown in the table below. In the retardation layer 2, the orientation of the molecular axis of the liquid crystal compound continuously changed in the direction from one end (left end) of each layer to the other end (right end).

[0081] <Twist Layer> A TAC (celluloacylate film) measuring 1000 mm wide x 200 mm long was prepared as a support. The support was passed through a dielectric heating roll at 60°C to raise the film surface temperature to 40°C, and then an alkaline solution having the composition shown below was applied to one side of the film using a bar coater in an amount of 14 mL / m. ２ The coating was then allowed to stand for 10 seconds under a steam-type far-infrared heater (manufactured by Noritake Co., Ltd.) heated to 110°C. Next, pure water was applied at a rate of 3 mL / m using the same bar coater. ２ Next, the film was washed with water using a fountain coater and then dried with an air knife three times, and then allowed to stay in a drying zone at 70°C for 5 seconds to dry, thereby preparing a saponified cellulose acylate film 1. The in-plane retardation Re of the cellulose acylate film 1 was measured with an AxoScan and found to be 1 nm.

[0082] Alkaline solution ------------------------------------------------ Potassium hydroxide 4.7 parts by mass Water 15.7 parts by mass Isopropanol 64.8 parts by mass Surfactant (C 16 H 33 O(CHCHO) 10 H) 1.0 part by mass Propylene glycol 14.9 parts by mass

[0083] The saponified surface of the saponified cellulose acylate film 1 (resin layer) was coated with a composition for forming an alignment film having the following composition 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.

[0084] ------------------------------------------------------------------ Composition of composition for forming alignment film ------------------------------------------------------------------ Modified polyvinyl alcohol 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 ------------------------------------------------------------------

[0085] Modified polyvinyl alcohol (see structural formula below)

[0086]

[0087] The surface of the orientation film of the cellulose acylate film 1 on which the orientation film was formed 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 times: 1 round trip) in a direction rotated 90° clockwise from the longitudinal direction of the cellulose acylate film 1 as viewed from the orientation film surface.

[0088] Next, the following components were mixed to prepare a composition for forming a twist layer having the following composition: ------------------------------------------------ Twist layer forming composition ------------------------------------------------ Mixture 1: 100 parts by mass Alignment control agent 1: 0.05 parts by mass Alignment control agent 2: 0.02 parts by mass Right-handed chiral agent LC756 (manufactured by BASF) adjusted according to the target pitch number x and film thickness y Polymerization initiator (IRGACURE OXE01, manufactured by BASF) 1.0 part by mass Solvent (methyl ethyl ketone) amount to give a solute concentration of 20% by mass ------------------------------------------------

[0089] The following composition for forming a twist layer was applied to the rubbed surface of the alignment film on the cellulose acylate film 1 using a wire bar. The coating was then dried and placed on a hot plate at 50°C. The coating was then heated to 1000°C in an environment with an oxygen concentration of 1000 ppm or less using an electrodeless lamp "D bulb" (60 mW / cm) manufactured by Fusion UV Systems. 2 The liquid crystal layer was irradiated with ultraviolet light for 6 seconds using a 1000 kJ / cm² film, and the liquid crystal phase was fixed to obtain a twisted layer 1.

[0090] Twist layer 2 was produced in the same manner as twist layer 1, except that the pitch number x and film thickness y were adjusted to be as shown in Table 2 below.

[0091] <Preparation of Reflective Film> A linearly polarized reflective film (reflective layer) and any of the retardation layers 1-2 and twist layers 1-2 prepared above were bonded to a polycarbonate substrate (PC substrate) measuring 1000 mm wide x 200 mm long via an adhesive layer (OCA) as shown in Table 2 below, to prepare reflective films 1-4 used in Examples 1-4 and reflective film 5 used in Comparative Example 1. The linearly polarized reflective film was bonded to the polycarbonate substrate so that the in-plane slow axis direction of the optically anisotropic layer in the linearly polarized reflective film was perpendicular to the horizontal direction of the polycarbonate substrate. In other words, the reflection axis of the linearly polarized reflective film was perpendicular to the horizontal direction of the reflective film (see FIG. 4). As described above, the molecular axes of the liquid crystal compounds in the retardation layers 1-2 rotated continuously along one direction, and this direction was parallel to the horizontal direction of the reflective film. That is, the one direction was perpendicular to the direction of the in-plane slow axis of the optically anisotropic layer in the linearly polarized reflective film. Furthermore, when the retardation layers 1 and 2 and the twist layers 1 and 2 were bonded together, the support and the alignment film were also bonded together, and the lateral direction of the support was aligned with the lateral direction of the polycarbonate substrate. Furthermore, when the retardation layers 1 and 2 and the twist layers 1 and 2 were bonded together, the support was positioned on the outside (opposite the polycarbonate substrate).

[0092] <Evaluation> Assuming a head-up display system using a pillar-to-pillar combiner, an iPad (registered trademark) was placed under the reflective film prepared above so that the angle of incidence was 45°. More specifically, as shown in Fig. 12, which is a schematic side view of the head-up display system used in the examples, an iPad (registered trademark) 50 was placed under a reflective film 52 so that the angle of incidence θ1 of light emitted (projected light) from the iPad (registered trademark) 50, which functions as a light source, with respect to the reflective film 52 was 45° and the angle of reflection θ2 was 45°. In this case, as shown in Fig. 13, which is a schematic view of the head-up display system used in the examples when observed from above, the position of the iPad (registered trademark) 50 was changed, and images emitted from each position and displayed on the reflective film 52 were observed. 13, the iPad (registered trademark) 50 was placed in front of the observer OB at position 1, at position 2 so that the incident angle θ3 of light emitted from the iPad (registered trademark) 50 was 15°, and at position 3 so that the incident angle θ4 of light emitted from the iPad (registered trademark) 50 was 30°, and the image displayed on the reflective film 52 was observed. Note that the polarized light emitted from the iPad (registered trademark) was circularly polarized light, and a λ / 4 film was sandwiched between the iPad (registered trademark) and the retardation layer so that the polarized light incident on the retardation layer was appropriately P-polarized light.

[0093] In the head-up display system obtained above, white letters on a black background were displayed on the iPad (registered trademark), and the position of the iPad (registered trademark) was changed as described above, and the HUD image at each position was evaluated according to the following criteria: A: Bright, letters are easy to see. B: Slightly dim, but letters are visible (acceptable level). C: Dark, letters are difficult to see.

[0094] In Table 2, the "In-plane Re [nm]" column in the "Retardation Layer" column represents the in-plane retardation (nm) of the retardation layer at a wavelength of 550 nm. The "Left Edge Angle [°]" column in the "Retardation Layer" column represents the angle (°) of the molecular axis of the liquid crystal compound relative to the horizontal direction at the left edge position of the retardation layer in the horizontal direction (the front position of the observer OB in FIG. 13). The "Right Edge Angle [°]" column in the "Retardation Layer" column represents the angle (°) of the molecular axis of the liquid crystal compound relative to the horizontal direction at the right edge position of the retardation layer in the horizontal direction. In Table 2, in the "Evaluation" column, the "0 °" column represents the evaluation results when the iPad (registered trademark) was placed at the above-mentioned arrangement position 1, the "15 °" column represents the evaluation results when the iPad (registered trademark) was placed at the above-mentioned arrangement position 2, and the "30 °" column represents the evaluation results when the iPad (registered trademark) was placed at the above-mentioned arrangement position 3.

[0095]

[0096] As shown in Table 2 above, it was confirmed that the desired effects were obtained when the reflective film of the present invention was used. Furthermore, a comparison between Examples 1 and 2 confirmed that better effects were obtained when the in-plane retardation of the retardation layer at a wavelength of 550 nm was 210 to 340 nm and the angle between the molecular axis of the liquid crystal compound located at one end in one direction of the retardation layer and the molecular axis of the liquid crystal compound located at the other end in the same direction was 7 to 15°. Furthermore, a comparison between Examples 3 and 4 confirmed that better effects were obtained when formulas (3) and (4) were satisfied.

[0097] 10, 100 Head-up display system 12, 112 Projector 14, 114, 52 Reflective film 16, 116 Substrate 18, 118 Linearly polarized light reflective layer 18a Optically anisotropic layer 18a 18b Isotropic layer 20 Polarization conversion layer 30 Retardation layer 32 Liquid crystal compound 40 Photo-alignment film 42A, 42B Polarizer 44A, 44B Mask 50 iPad (registered trademark)

Claims

1. A reflective film having a linearly polarized light reflecting layer including an optically anisotropic layer and an isotropic layer, and a polarization conversion layer, wherein the polarization conversion layer satisfies the following requirement (A) or (B), and the width of the reflective film in a direction orthogonal to the in-plane slow axis of the optically anisotropic layer is 300 mm or more. (A) The polarization conversion layer is a retardation layer, the retardation layer contains a liquid crystal compound, and the direction of the molecular axis of the liquid crystal compound changes continuously or stepwise along one direction in the plane of the retardation layer. (B) The polarization conversion layer is a layer in which the helical alignment structure of a liquid crystal compound twisted and aligned along a helical axis extending in the thickness direction is fixed. When the number of pitches of the helical alignment structure is x and the film thickness of the polarization conversion layer is y (μm), the relationships of Formula (1) and Formula (2) are satisfied. Formula (1) 0.010 ≦ x < 0.100 Formula (2) 0.5 ≦ y ≦ 5.0 2. The reflective film according to claim 1, wherein the polarization conversion layer satisfies the requirement (A), the in-plane retardation of the retardation layer at a wavelength of 550 nm is 100 to 500 nm, and the angle formed by the molecular axis of the liquid crystal compound located at one end in the one direction and the molecular axis of the liquid crystal compound located at the other end in the one direction is 3 to 40°.

3. The reflective film according to claim 1, wherein the polarization conversion layer satisfies the requirement (A), the in-plane retardation of the retardation layer at a wavelength of 550 nm is 210 to 340 nm, and the angle formed by the molecular axis of the liquid crystal compound located at one end in the one direction and the molecular axis of the liquid crystal compound located at the other end in the one direction is 7 to 15°.

4. The reflective film according to claim 1, wherein the polarization conversion layer satisfies the requirement (B), and the number of pitches x of the helical alignment structure and the film thickness y (μm) of the polarization conversion layer satisfy the relationships of Formula (3) and Formula (4). Formula (3) 0.014 ≦ x ≦ 0.050 Formula (4) 0.6 ≦ y ≦ 4.0 5. A head-up display system having the reflective film according to any one of claims 1 to 4 and a projector that irradiates projection light onto the reflective film.

6. The head-up display system according to claim 5, wherein the projector emits P-polarized light as the projection light.

Images