Reflective film, windshield and heads-up display system

Abstract

This invention provides a reflective film, a windshield, and a head-up display system capable of suppressing ghosting in displayed images. The reflective film comprises a linearly polarized light reflecting layer formed by stacking optically anisotropic and isotropic layers, and a polarization conversion layer. The polarization conversion layer satisfies any of the following conditions: (A) The polarization conversion layer is a phase retardation layer with a frontal retardation of 30 nm to 200 nm, and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflecting layer is within 35°. (B) The polarization conversion layer is a layer obtained by immobilizing the helical alignment structure of a liquid crystal compound, and the pitch number x of the helical alignment structure and the film thickness y (in μm) of the polarization conversion layer satisfy all of the following relationships: (i) 0.1 ≤ x ≤ 1.0 (ii) 0.5 ≤ y ≤ 3.0 (iii) 3000 ≤ (1560 × y) / x ≤ 50000.

Description

Technical Field

[0001] The present invention relates to a reflective film that can be used as a combiner in a head-up display system, and a windshield and a head-up display system having the reflective film. Background Technology

[0002] Currently, there is a technology known as a head-up display or head-up display system that projects images onto the windshield of vehicles and other objects, providing drivers with various information such as maps, speed, and vehicle status.

[0003] In a head-up display (HUD) system, a virtual image projected onto the windshield, containing all the aforementioned information, can be observed by the driver and other passengers. The virtual image is positioned further outward and forward than the windshield. Typically, the virtual image is positioned at least 1000mm forward of the windshield, on the outermost side of the windshield. Therefore, the driver can obtain all the aforementioned information while observing the surrounding environment without significantly shifting their line of sight. Thus, when using a HUD system, it is expected that drivers can drive more safely while obtaining various information.

[0004] Head-up display (HUD) systems can be constructed by forming a semi-reflective film (reflective coating) on ​​the windshield. Various semi-reflective films that can be used in HUD systems have been proposed.

[0005] Patent Document 1 describes a semi-reflective mirror for projected image display, which includes a selective reflective layer that selectively reflects light of a certain wavelength. In the semi-reflective mirror, the selective reflective layer has a selective reflection center wavelength of 650 to 780 nm, which is the shortest wavelength in the visible light wavelength range.

[0006] The semi-reflective mirror for projected image display described in Patent Document 1 is, for example, assembled into a windshield to form a head-up display system. In addition to high visible light transmittance, the windshield (combiner) constituting the head-up display system is also required to allow visual recognition of images even when the driver is wearing polarized sunglasses.

[0007] The reflected light from objects like the hood of a car or puddles on the road, which can obstruct driving, is primarily S-polarized light. Polarized sunglasses, therefore, have the function of blocking S-polarized light. Thus, by wearing polarized sunglasses, you will not see the glare from reflected light from oncoming vehicles' hoods or puddles.

[0008] The semi-reflective mirror for displaying projected images described in Patent Document 1 is a semi-reflective mirror that reflects p-polarized light to display projected images 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] Previous technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2019-012211 Summary of the Invention

[0012] The technical problem to be solved by the invention

[0013] Here, Patent Document 1 describes a semi-reflective mirror for projected image display that has a linearly polarized light reflecting layer made of thin films with different refractive indices stacked together, serving as a selective reflecting layer for light with a selective reflection wavelength.

[0014] In head-up displays (HUDs) that reflect P-polarized light, when a reflective film with a linearly polarized light reflective layer is assembled onto a windshield, a ghosting problem occurs when viewed from an angle. This ghosting problem is particularly severe in wide-viewing-angle HUDs.

[0015] The objective of this invention is to provide a reflective film capable of suppressing ghosting in displayed images, a windshield using the reflective film, and a head-up display system.

[0016] means for solving technical problems

[0017] [1] A reflective film comprising a linearly polarized light reflective layer formed by stacking an optically anisotropic layer and an isotropic layer, and a polarization conversion layer.

[0018] The polarization conversion layer satisfies any of the following conditions:

[0019] (A) The polarization conversion layer is a phase retardation layer with a frontal retardation of 30nm to 200nm at a wavelength of 550nm, and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflecting layer is within 35°.

[0020] (B) The polarization conversion layer is a layer obtained by immobilizing the helical alignment structure of the liquid crystal compound. The pitch number x of the helical alignment structure and the film thickness y (in μm) of the polarization conversion layer satisfy all of the following relationships:

[0021] (i) 0.1 ≤ x ≤ 1.0

[0022] (ii) 0.5 ≤ y ≤ 3.0

[0023] (iii)3000≤(1560×y) / x≤50000.

[0024] [2] According to the reflective film described in [1], wherein,

[0025] The polarization conversion layer is a phase difference layer with a frontal delay of 50nm to 120nm at a wavelength of 550nm, and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflecting layer is within 20°.

[0026] [3] According to the reflective film described in [1] or [2], wherein,

[0027] The number of layers in the linearly polarized light reflective layer, including the optical anisotropic layer and the isotropic layer, ranges from 10 to 60.

[0028] [4] A windshield having:

[0029] The reflective film described in any one of [1] to [3], and

[0030] The first curved glass and the second curved glass that hold the reflective film.

[0031] A linearly polarized light reflecting layer, a polarization light conversion layer, and a first curved glass are sequentially stacked from the convex side of the second curved glass.

[0032] [5] A head-up display system having:

[0033] [4] the windshield; and

[0034] A projector that projects p-polarized light onto the second curved glass side of the windshield.

[0035] Invention Effects

[0036] According to the present invention, it is possible to provide a reflective film, a windshield, and a head-up display system that can suppress ghosting of displayed images. Attached Figure Description

[0037] Figure 1 This is a schematic diagram illustrating an example of the reflective film of the present invention.

[0038] Figure 2 This diagram illustrates the angle between the direction of the transmission axis of the linearly polarized light reflector and the direction of the slow axis of the phase difference layer.

[0039] Figure 3 It is a graph showing the relationship between the slow axis angle of the phase difference layer, the frontal Re of the phase difference layer, and the evaluation of ghosting.

[0040] Figure 4This is a schematic diagram illustrating an example of a head-up display having the reflective film of the present invention.

[0041] Figure 5 This is a schematic diagram illustrating an example of a windshield having the reflective film of the present invention. Detailed Implementation

[0042] The reflective film, windshield, and head-up display system of the present invention will now be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0043] Furthermore, the figures described below are illustrative for illustrating the present invention, and the present invention is not limited to the figures shown below.

[0044] Furthermore, the "~" sign indicating a range of values ​​includes the values ​​on both sides. For example, ε1 being α1 to β1 means that the range of ε1 includes both α1 and β1, which, in mathematical notation, is α1 ≤ ε1 ≤ β1.

[0045] Unless otherwise stated, angles such as "angles expressed in specific numerical values", "parallel", "perpendicular" and "orthogonal" are included within the generally permissible range of error in the applicable technical field.

[0046] In addition, "same" includes the error range that is generally permissible in the relevant technical field, and "the entire surface" and the like also include the error range that is generally permissible in the applicable technical field.

[0047] Unless otherwise stated, the term "light" refers to visible and natural (unpolarized) light. Visible light is electromagnetic light with wavelengths visible to the human eye, typically defined as light in the wavelength range of 380–780 nm. Invisible light is light with wavelengths below 380 nm or above 780 nm.

[0048] In addition, and not limited to this, the wavelength range of visible light from 420 to 490 nm is blue (B) light, the wavelength range of 495 to 570 nm is green (G) light, and the wavelength range of 620 to 750 nm is red (R) light.

[0049] "Visible light transmittance" is defined as the visible light transmittance of light source A as specified in JIS (Japanese Industrial Standard) R 3212:2015 (Test Method for Safety Glass for Automobiles). That is, it is the transmittance of each wavelength in the range of 380–780 nm measured using a spectrophotometer with light source A. The transmittance is then calculated by multiplying the transmittance of each wavelength by a weighted average of the transmittance obtained from the wavelength distribution and wavelength intervals of the luminous efficacy according to the CIE (International Commission on Illumination) luminance adaptation standard.

[0050] The term is used only when referred to as "reflected light" or "transmitted light" to mean both scattered and diffracted light.

[0051] p-polarized light refers to polarized light that vibrates in a direction parallel to the plane of incidence. The plane of incidence is the surface perpendicular to the reflecting surface (such as the surface of a windshield) and includes both the incident and reflected rays. In p-polarized light, the plane of vibration of the electric field vector is parallel to the plane of incidence.

[0052] The forward phase difference is measured using an AxoScan manufactured by Axometrics. Unless otherwise specified, the measurement wavelength is set to 550 nm. The forward phase difference can also be measured using a KOBRA 21ADH or WR (manufactured by Oji Measurement Equipment Co., Ltd.) by incident light of wavelengths within the visible light range along the normal direction of the film. When selecting the measurement wavelength, the wavelength selection filter can be changed manually, or the measurement value can be converted using a program.

[0053] A "projection image" is not the scenery in front of or around the viewer, but rather an image projected onto the windshield based on light from a projector. When observed by an observer, the projection image is perceived as a virtual image that appears in front of the reflective film on the windshield and is visible.

[0054] An "image" refers to a picture displayed on the projection device of a projector or a picture drawn on an intermediate image screen, etc. In contrast to a virtual image, an image is a real image.

[0055] Images and projected images can be monochrome images, multicolor images with two or more colors, or full-color images.

[0056] [Reflective film]

[0057] The reflective film of the present invention comprises a linearly polarized light reflective layer formed by stacking optically anisotropic and isotropic layers, and a polarization conversion layer.

[0058] The polarization conversion layer satisfies any of the following conditions:

[0059] (A) The polarization conversion layer is a phase difference layer with a frontal retardation of 30nm to 200nm, and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflecting layer is within 35°.

[0060] (B) The polarization conversion layer is a layer obtained by immobilizing the helical alignment structure of the liquid crystal compound. The pitch number x of the helical alignment structure and the film thickness y (in μm) of the polarization conversion layer satisfy all of the following relationships:

[0061] (i) 0.1 ≤ x ≤ 1.0

[0062] (ii) 0.5 ≤ y ≤ 3.0

[0063] (iii)3000≤(1560×y) / x≤50000.

[0064] Figure 1 This is a schematic diagram illustrating an example of the reflective film of the present invention. (As shown) Figure 1 As shown, the reflective film 10 has a linearly polarized light reflective layer 12 formed by alternating layers of optical anisotropic layer 12a and isotropic layer 12b, and a polarization conversion layer 11.

[0065] <Linearly polarized light reflector>

[0066] In the linearly polarized light reflecting layer 12, the refractive index n along the slow axis of the optical anisotropy layer 12a is... e1 The refractive index n is greater than that of the isotropic layer 12b o2 The refractive index n in the direction orthogonal to the slow axis of the optical anisotropy layer 12a o1 The refractive index n of the isotropic layer 12b o2 The general structure is similar. The slow axes of the multiple optical anisotropic layers 12a are stacked in a parallel manner. Therefore, in a certain direction, the refractive index (n) becomes... e1 High layer and refractive index (n) o2 The lower-index layered state. On the other hand, in the direction orthogonal to this direction, the layers are stacked with the same refractive index.

[0067] It is known that films composed of alternating layers of low-refractive-index and high-refractive-index layers reflect light of a specific wavelength through structural interference between numerous low-refractive-index and high-refractive-index layers. Therefore, the linearly polarized light reflecting layer reflects linearly polarized light along the slow axis (the direction of high refractive index) of the optical anisotropic layer 12a, while allowing linearly polarized light in the direction orthogonal to the slow axis to pass through.

[0068] That is, the linearly polarized light reflective layer 12 is a layer that selectively reflects linearly polarized light within a specific wavelength range. The linearly polarized light reflective layer 12 preferably exhibits selective reflection within a portion of the visible light wavelength range. The linearly polarized light reflective layer 12 can reflect light, for example, used to display projected images. Furthermore, the reflective film 10 may also be a structure having multiple linearly polarized light reflective layers 12 corresponding to various wavelength ranges.

[0069] The linearly polarized light reflective layer 12 allows unreflected linearly polarized light to pass through. Therefore, the reflective film 10, by having the linearly polarized light reflective layer 12, allows a portion of light to pass through within the wavelength range reflected by the linearly polarized light reflective layer 12. Thus, it is preferable as it does not easily cause color deterioration of the light transmitted through the reflective film 10, nor does it easily reduce the transmittance of visible light.

[0070] In a linearly polarized light reflecting layer composed of stacked low-refractive-index and high-refractive-index layers, the reflected wavelength and reflectivity can be adjusted by the refractive index difference, thickness, and number of stacks between the low-refractive-index and high-refractive-index layers. Specifically, by setting the thickness d of the low-refractive-index and high-refractive-index layers to d = λ / (4 × n) based on the wavelength λ and refractive index n of the reflected light, the wavelength λ of the reflected light can be adjusted. Furthermore, since the reflectivity increases with the number of stacked low-refractive-index and high-refractive-index layers, the reflectivity can be adjusted by changing the number of stacks. Additionally, the width of the reflection bandwidth can be adjusted by the refractive index difference between the low-refractive-index and high-refractive-index layers.

[0071] The materials and methods for fabricating linearly polarized light reflective layers can be, for example, those described in Japanese Patent Application Publication No. 9-506837. Specifically, various materials can be used to form linearly polarized light reflective layers if processing is performed under conditions selected to obtain a refractive index relationship. Generally, the first material must have a different refractive index than the second material in the selected direction. This difference in refractive index can be achieved by various methods, including stretching, extrusion molding, or coating during or after film formation. Furthermore, similar rheological properties (e.g., melt viscosity) are preferred so that the two materials can be extruded simultaneously.

[0072] Commercially available products can be used as linearly polarized light reflective layers. Commercially available products can also be laminates that function as reflective polarizers and temporary supports. Examples of commercially available products include, for instance, commercially available optical films sold as DBEF (registered trademark) (manufactured by 3M) and APF (Advanced Polarizing Film (manufactured by 3M)).

[0073] The thickness of the linearly polarized light reflective layer is preferably in the range of 2.0 μm to 50 μm, and more preferably in the range of 8.0 μm to 30 μm.

[0074] In addition, the number of optical anisotropic and isotropic layers of the linearly polarized light reflective layer can be appropriately set according to the calculated reflectivity, but it is preferably 10 to 60 layers.

[0075] <Polarization conversion layer>

[0076] The polarization conversion layer 11 is (A) a phase retardation layer with a front retardation of 30nm to 200nm, and the angle between the direction of the slow axis and the direction of the transmission axis of the linear polarization reflection layer is within 35°. Alternatively, the polarization conversion layer 11 is (B) a layer obtained by immobilizing the helical alignment structure of the liquid crystal compound, where the pitch number x of the helical alignment structure and the film thickness y (in μm) of the polarization conversion layer satisfy all of the following relationships.

[0077] (i) 0.1 ≤ x ≤ 1.0

[0078] (ii) 0.5 ≤ y ≤ 3.0

[0079] (iii)3000≤(1560×y) / x≤50000

[0080] As mentioned above, in head-up displays that reflect p-polarized light, when a reflective film with a linearly polarized light reflective layer is assembled onto the windshield, a problem of ghosting occurs when viewed from an angle. This ghosting problem is particularly severe in head-up displays with wide viewing angles.

[0081] When p-polarized light is incident on the windshield, the reflection caused by the glass becomes very small. Therefore, it is possible to eliminate ghosting caused by light reflected from the surface of the windshield.

[0082] However, when linearly polarized light is incident obliquely onto the linearly polarized light reflector layer, the polarization state of the transmitted light changes to elliptically polarized light, etc. The s-polarized component of the elliptically polarized light is reflected by the interface of the glass on the back side (the side opposite to the surface from which the projected image from the projector is incident), and is perceived visually as an image. Therefore, the image reflected by the linearly polarized light reflector layer and the image reflected by the interface of the glass on the back side are perceived visually as a ghost image.

[0083] In contrast, in this invention, the reflective film 10 includes a polarization conversion layer 11 with a defined structure, arranged such that the surface side of the windshield (the surface from which the projected image from the projector is incident) serves as a linearly polarized light reflective layer 12, and the back side serves as the polarization conversion layer 11. In this structure, when linearly polarized light (p-polarized light) is obliquely incident on the linearly polarized light reflective layer 12, the transmitted light (s-polarized light) is converted into elliptically polarized light (or similar light) through the linearly polarized light reflective layer 12 and then incident on the polarization conversion layer 11. The polarization conversion layer 11, by satisfying the above-described structure, converts the incident elliptically polarized light (or similar light) into p-polarized light. Therefore, when p-polarized light is incident on the back side of the glass, reflection from the glass can be suppressed, and ghosting can be suppressed.

[0084] Furthermore, by satisfying the above structure through the polarization conversion layer 11, light incident on the reflective film 10 at an incident angle of 0 degrees is kept as p-polarized light, thus resulting in good ghosting over a wide range.

[0085] Furthermore, the polarization state of s-polarized light incident from the outside of the windshield is changed by the linearly polarized light reflective layer 12. In contrast, since the reflective film 10 has a polarization conversion layer 11, the s-polarized light passing through the reflective film 10 can maintain its s-polarization, thus improving the adaptability of polarized sunglasses.

[0086] Below, we will describe the case where the polarization conversion layer 11 is the phase difference layer described above as polarization conversion layer A, and the case where the polarization conversion layer 11 is a layer obtained by fixing a spiral orientation structure as polarization conversion layer B.

[0087] (Polarization conversion layer A)

[0088] The polarization conversion layer A is a phase difference layer with a frontal delay of 30nm to 200nm, and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflecting layer is within 35°.

[0089] The retardation layer only needs to have a frontal retardation of 30 nm to 200 nm, and there are no particular restrictions. It can be selected appropriately according to the purpose. Examples of retardation layers include stretched polycarbonate films, stretched norbornene polymer films, transparent films containing birefringent inorganic particles such as strontium carbonate and oriented accordingly, thin films of inorganic dielectrics deposited obliquely on a support, films in which polymeric liquid crystal compounds are uniaxially oriented and their orientation is fixed, and films in which liquid crystal compounds are uniaxially oriented and their orientation is fixed.

[0090] Among them, a film that uniaxially aligns and fixes the orientation of a polymeric liquid crystal compound is appropriately exemplified as a phase retardation layer.

[0091] Such a phase retardation layer can be formed as follows: a liquid crystal composition containing a polymeric liquid crystal compound is coated on the surface of a temporary support or alignment layer. The polymeric liquid crystal compound in the liquid crystal composition is then oriented in a nematic state and fixed by curing.

[0092] The phase retardation layer can also be obtained by coating a composition containing a polymer liquid crystal compound onto the surface of a temporary support or alignment layer, forming a nematic alignment in a liquid crystal state, and then fixing the alignment by cooling.

[0093] The thickness of the retardation layer is not limited, but is preferably 0.2 μm to 300 μm, more preferably 0.5 μm to 150 μm, and even more preferably 1.0 μm to 80 μm. The thickness of the retardation layer formed from the liquid crystal composition is not particularly limited, but is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 5.0 μm, and even more preferably 0.7 μm to 2.0 μm.

[0094] The frontal delay of the retardation layer at a wavelength of 550 nm is preferably 50 nm to 120 nm, more preferably 70 nm to 120 nm. By setting the frontal delay of the retardation layer to this range, ghosting can be suppressed more appropriately.

[0095] like Figure 2As shown, the phase retardation layer is configured such that the angle β between its slow axis direction and the transmission axis direction of the linearly polarized light reflecting layer is within 35°. The angle β is preferably within 20°, more preferably within 15°. By setting the angle β within this range, ghosting can be suppressed more appropriately. Furthermore, in the following description, when viewing the reflective film 10 from the front side, the transmission axis direction of the linearly polarized light reflecting layer is set to 0°, and the angle between the slow axis direction of the phase retardation layer and the transmission axis direction of the linearly polarized light reflecting layer is expressed as clockwise (+) and counterclockwise (-).

[0096] The results of this simulation, which explores the relationship between the frontal delay and angle β of the phase retardation layer and ghosting, are presented below. Figure 3 .exist Figure 3 In the diagram, the horizontal axis represents the angle β between the slow axis direction of the retardation layer and the transmission axis direction of the linearly polarized light reflecting layer, and the vertical axis represents the frontal retardation of the retardation layer, where the value represents the proportion of reflected light from the back of the glass in the reflected light. This value corresponds to the value evaluated in the ghosting assessment of the embodiments described later.

[0097] In the simulation, the linearly polarized light reflector was modeled as a stack consisting of alternating layers of an optically anisotropic layer composed of PEN with a refractive index of 1.86 along the slow axis and an isotropic layer composed of coPEN with a refractive index of 1.64. The film thickness was appropriately set and modeled with a visible light reflectance of 20%. Ghosting was evaluated when viewed horizontally from a polar angle of 20°.

[0098] Depend on Figure 3 It can be seen that when the frontal delay is 30nm to 200nm and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflector is within 35°, the ghosting is reduced.

[0099] (Polarization conversion layer B)

[0100] The polarization conversion layer B is a layer obtained by immobilizing the helical alignment structure (helical structure) of the liquid crystal compound. The pitch number x of the helical alignment structure and the film thickness y (in μm) of the polarization conversion layer satisfy all the following relationships.

[0101] (i) 0.1 ≤ x ≤ 1.0

[0102] (ii) 0.5 ≤ y ≤ 3.0

[0103] (iii)3000≤(1560×y) / x≤50000

[0104] Furthermore, one pitch of the helical structure of the liquid crystal compound is one turn of the helix of the liquid crystal compound. That is, the pitch number is defined as the state in which the direction vector of the helically oriented liquid crystal compound (or the major axis direction if it is a rod-shaped liquid crystal) is rotated by 360°.

[0105] When the polarization conversion layer B has a helical structure of a liquid crystal compound, it exhibits optical rotation and birefringence for visible light with wavelengths shorter than the reflection peak wavelength in the infrared region. Therefore, polarized light in the visible region can be controlled. By setting the pitch number x of the helical orientation structure of the polarization conversion layer B and the film thickness y of the polarization conversion layer within the aforementioned range, optical compensation can be performed using the polarization conversion layer B. Therefore, as described above, transmitted light, which has become elliptically polarized light, is converted into p-polarized light by the linearly polarized light reflecting layer 12. As a result, p-polarized light is incident on the back-side glass, thus suppressing reflections from the glass and suppressing ghosting.

[0106] By utilizing the helical structure of the liquid crystal compound that satisfies equations (i) to (iii), the polarization conversion layer B exhibits optical rotation and birefringence in the visible light spectrum. In particular, by setting the pitch P of the helical structure of the polarization conversion layer B to a length corresponding to the pitch P of the cholesteric liquid crystal layer, which selectively reflects wavelengths in the long-wavelength infrared region, it exhibits high optical rotation and birefringence in the short-wavelength visible light spectrum.

[0107] The relation (i) is “0.1≤x≤1.0”.

[0108] When the pitch number x of the helical structure is less than 0.1, it results in undesirable conditions such as insufficient optical rotation and birefringence.

[0109] In addition, if the pitch number x of the helical structure exceeds 1.0, it will result in excessive optical rotation and birefringence, and the inability to obtain the desired elliptically polarized light.

[0110] The relation (ii) is “0.5≤y≤3.0”.

[0111] When the thickness y of the polarization conversion layer B is less than 0.5 μm, the film thickness is too thin, resulting in undesirable conditions such as insufficient optical rotation and birefringence.

[0112] If the thickness y of the polarization conversion layer B exceeds 3.0 μm, it will result in excessive optical rotation and birefringence, failure to obtain the desired elliptically polarized light, easy occurrence of misalignment, and other adverse effects on manufacturing.

[0113] The relation (iii) is “3000≤(1560×y) / x≤50000”.

[0114] When “(1560×y) / x” is less than 3000, adverse situations such as excessive optical rotation and inability to obtain the desired polarized light will occur.

[0115] If "(1560×y) / x" exceeds 50000, it will result in problems such as insufficient optical rotation and inability to obtain the desired polarized light.

[0116] In this invention, the pitch number x of the spiral structure of the polarization conversion layer B is preferably 0.1 to 0.5, and the film thickness y is preferably 1.0 μm to 3.0 μm.

[0117] That is, the preferred polarization conversion layer B has a spiral structure with a long pitch P and a small number of pitches x.

[0118] Specifically, the pitch P of the preferred spiral of the polarization conversion layer B is equal to the pitch P of the cholesteric liquid crystal layer that selects a long-wavelength infrared region for reflection, and the number of pitches x is small. More specifically, the pitch P of the preferred spiral of the preferred polarization conversion layer B is equal to the pitch P of the cholesteric liquid crystal layer that selects a wavelength of 3000–10000 nm for reflection, and the number of pitches x is small.

[0119] Because the selective reflection center wavelength corresponding to the pitch P of this polarization conversion layer B is much longer than the wavelength of visible light, it more appropriately exhibits the aforementioned optical rotation and birefringence relative to visible light. Therefore, it can further improve the ghosting suppression effect.

[0120] Such a polarization conversion layer B can be formed in a manner similar to that of a known cholesterol-type liquid crystal layer. However, when forming the polarization conversion layer B, it is necessary to adjust the liquid crystal compound used, the chiral additive used, the amount of chiral additive added, and the film thickness, so that the pitch number x and the film thickness y [μm] of the helical structure in the polarization conversion layer B satisfy all the relationships (i) to (iii).

[0121] <A layer obtained by immobilizing the helical orientation structure (helical structure) of a liquid crystal compound>

[0122] A layer obtained by immobilizing the helical orientation structure (helical structure) of a liquid crystal compound is called a cholesterol-type liquid crystal layer, which refers to a layer in which a cholesterol-type liquid crystal phase is fixed.

[0123] A cholesterol-type liquid crystal layer is simply a layer that maintains the orientation of a liquid crystal compound that is a cholesterol-type liquid crystal phase. Typically, a cholesterol-type liquid crystal layer is formed by polymerizing and curing a polymerizable liquid crystal compound in a cholesterol-type liquid crystal phase orientation through processes such as ultraviolet irradiation and heating. This process creates a non-flowing layer that remains oriented in a state unaffected by external fields or forces. Furthermore, in a cholesterol-type liquid crystal layer, it is sufficient to maintain the optical properties of the cholesterol-type liquid crystal phase within the layer; the liquid crystal compound itself may no longer exhibit liquid crystal properties. For example, polymerizable liquid crystal compounds can be increased in molecular weight through curing reactions, thus losing their liquid crystal properties.

[0124] The selective reflection center wavelength λ of a cholesterol-type liquid crystal layer depends on the pitch P (equal to the period of the helix) of the helical structure (helical orientation structure) in the cholesterol-type liquid crystal phase, and follows the relationship between the average refractive index n of the cholesterol-type liquid crystal layer and λ = n × P. This equation shows that the selective reflection center wavelength can be adjusted by regulating the values ​​of n and / or P.

[0125] In other words, the pitch P (helix 1 pitch) of the helical structure is the length of one turn of the helix along the helical axis, that is, the length of the helical axis along which the directional vector (or the major axis direction if it is a rod-shaped liquid crystal) of the liquid crystal compound constituting the cholesterol-type liquid crystal phase rotates 360°. Typically, the helical axis of a cholesterol-type liquid crystal layer coincides with the thickness direction of the cholesterol-type liquid crystal layer.

[0126] The selective reflection center wavelength and half-width of a cholesterol-type liquid crystal layer can be calculated as follows, as an example.

[0127] When measuring the reflectance spectrum of a cholesterol-type liquid crystal layer from the normal direction using a spectrophotometer (Nippon Spectrophotometer, V-670), a transmittance reduction peak was observed in the selected reflectance band. The shorter wavelength of the two wavelengths representing the minimum transmittance of this peak and the intermediate (average) transmittance before the reduction is denoted as λ. l (nm), where the wavelength value on the longer wavelength side is set to λ. h When the wavelength is (nm), the selection of the reflection center wavelength λ and half-width Δλ can be expressed by the following formula.

[0128] λ=(λ l +λ h ) / 2Δλ=(λ h -λ l )

[0129] The selected reflection center wavelength obtained as described above is basically consistent with the wavelength located at the centroid of the reflection peak of the circularly polarized light reflection spectrum measured from the normal direction of the cholesterol-type liquid crystal layer.

[0130] Since the helical pitch of a cholesterol-type liquid crystal phase depends on the type and concentration of the chiral additive used with the polymerizable liquid crystal compound, the desired pitch can be obtained by adjusting it. Furthermore, the methods for determining the helix direction and pitch can be found in "Introduction to Liquid Crystal Chemistry Experiments," edited by the Japan Liquid Crystal Society, published by Sigma in 2007, page 46, and in "Liquid Crystal Handbook," edited by Maruzen of the Liquid Crystal Handbook Editorial Committee, page 196.

[0131] As described above, in the cholesterol-type liquid crystal layer used as polarization conversion layer B, the helical pitch is adjusted so that the selected reflection center wavelength becomes the long-wavelength infrared region.

[0132] (Method for fabricating cholesterol-type liquid crystal layers)

[0133] The following section describes the materials and manufacturing methods for cholesterol-type liquid crystal layers.

[0134] Examples of materials used to form the aforementioned cholesterol-type liquid crystal layer include liquid crystal compositions containing polymerizable liquid crystal compounds and chiral additives (optically active compounds). If necessary, the aforementioned liquid crystal composition, mixed with surfactants and polymerization initiators and dissolved in a solvent, can be coated onto a support, an alignment layer, or a cholesterol-type liquid crystal layer that forms the lower layer. After cholesterol alignment is achieved, the liquid crystal composition is cured and fixed to form the cholesterol-type liquid crystal layer.

[0135] (polymeric liquid crystal compound)

[0136] The polymerizable liquid crystal compound can be a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound, but a rod-shaped liquid crystal compound is preferred.

[0137] Examples of rod-shaped polymerizable liquid crystal compounds that form cholesterol-type liquid crystal layers include rod-shaped nematic liquid crystal compounds. Among these rod-shaped nematic liquid crystal compounds, methyleneamines, azo compounds, cyanobiphenyl compounds, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid esters, cyanophenylcyclohexane compounds, cyano-substituted phenylpyrimidine compounds, alkoxy-substituted phenylpyrimidine compounds, phenyldioxanes, diphenylacetylene compounds, and alkenylcyclohexylbenzylnitrile compounds are preferred. Not only low-molecular-weight liquid crystal compounds but also high-molecular-weight liquid crystal compounds can be used.

[0138] Polymerizable liquid crystal compounds are obtained by introducing polymerizable groups into a liquid crystal compound. Examples of polymerizable groups include unsaturated polymerizable groups, epoxy groups, and aziridine groups, with unsaturated polymerizable groups being preferred, and olefinic unsaturated polymerizable groups being particularly preferred. Polymerizable groups can be introduced into the molecules of the liquid crystal compound by various methods. The number of polymerizable groups in a polymerizable liquid crystal compound is preferably 1 to 6 per molecule, more preferably 1 to 3.

[0139] Examples of polymerizable liquid crystal compounds include those described in Makromol. Chem., Vol. 190, pp. 2255 (1989), Advanced Materials, Vol. 5, pp. 107 (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, WO95 / 22586, WO95 / 24455, WO97 / 00600, WO98 / 23580, WO98 / 52905, Japanese Patent Application Publication No. 1-272,551, Japanese Patent Application Publication No. 6-16616, Japanese Patent Application Publication No. 7-110,469, Japanese Patent Application Publication No. 11-80081, and Japanese Patent Application Publication No. 2001-328,973. Two or more polymerizable liquid crystal compounds may also be used in combination. Combining two or more polymerizable liquid crystal compounds can lower the orientation temperature.

[0140] Furthermore, the amount of polymerizable liquid crystal compound added to the liquid crystal composition is preferably 80 to 99.9% by mass relative to the mass of the solid components of the liquid crystal composition (excluding the solvent), more preferably 85 to 99.5% by mass, and particularly preferably 90 to 99% by mass.

[0141] (Chiral additives: optically active compounds)

[0142] Chiral auxiliaries have the function of inducing helical structures in cholesterol-type liquid crystal phases. Among chiral compounds, the direction of helix or helical pitch induced by the compound varies, thus the appropriate auxiliaries can be selected based on the intended purpose.

[0143] There are no particular restrictions on the use of chiral additives; known compounds may be used. Examples of chiral additives include compounds described in various publications such as the Liquid Crystal Device Handbook (Chapter 3, Items 4-3, TN and STN Chiral Additives, p. 199, edited by Committee 142 of the Japanese Society for the Promotion of Science, 1989), Japanese Patent Application Publication Nos. 2003-287623, 2002-302487, 2002-80478, 2002-80851, 2010-181852, and 2014-034581.

[0144] Chiral auxiliaries generally contain asymmetric carbon atoms, but axially asymmetric or planar asymmetric compounds that do not contain asymmetric carbon atoms can also be used as chiral auxiliaries. Examples of axially asymmetric or planar asymmetric compounds include binaphthyl, helicene, p-cycloaranes, and their derivatives.

[0145] Chiral auxiliaries can also have polymerizable groups. When both the chiral auxiliary and the liquid crystal compound have polymerizable groups, a polymer having repeating units derived from the liquid crystal compound and repeating units derived from the chiral auxiliary can be formed through the polymerization reaction of the chiral auxiliary and the liquid crystal compound. In this manner, the polymerizable groups possessed by the chiral auxiliary are preferably of the same type as those possessed by the liquid crystal compound. Therefore, the polymerizable groups of the chiral auxiliary are preferably unsaturated polymerizable groups, epoxy groups, or aziridine groups, more preferably unsaturated polymerizable groups, and particularly preferably olefinic unsaturated polymerizable groups.

[0146] Alternatively, chiral additives can also be liquid crystal compounds.

[0147] As chiral auxiliaries, isosorbide derivatives, isomannitol derivatives, and binaphthyl derivatives are preferred. For isosorbide derivatives, commercially available products such as BASF's LC756 can be used.

[0148] The content of the chiral additive in the liquid crystal composition is preferably 0.01 to 200 mol% of the polymerizable liquid crystal compound, more preferably 1 to 30 mol%. Furthermore, the content of the chiral additive in the liquid crystal composition refers to the concentration (mass %) of the chiral additive relative to the total solid components in the composition.

[0149] (Polymerization initiator)

[0150] The liquid crystal composition preferably contains a polymerization initiator. In the case of polymerization reaction by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator that can initiate polymerization reaction by ultraviolet irradiation.

[0151] Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Patent Nos. 2,367,661 and 2,367,670), ketol ethers (described in U.S. Patent No. 2,448,828), α-hydrocarbon-substituted aromatic ketol compounds (described in U.S. Patent No. 2,722,512), polynuclear quinone compounds (described in U.S. Patent Nos. 3,046,127 and 2,951,758), combinations of triarylimidazolium dimers and p-aminophenyl ketones (described in U.S. Patent No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent Application Publication No. 60-105,667 and U.S. Patent No. 4,239,850), and acylphosphine oxide compounds (described in Japanese Patent Application Publication No. 63-407). Japanese Published Publications No. 99, No. 5-29234, No. 10-95788, No. 10-29997, No. 2001-233842, No. 2000-80068, No. 2006-342166, No. 2013-114249, and No. 201 Japanese Patent Publication No. 4-137466, Japanese Patent Publication No. 4223071, Japanese Unexamined Patent Publication No. 2010-262028, Japanese Unexamined Patent Publication No. 2014-500852, oxime compounds (described in Japanese Unexamined Patent Publication No. 2000-66385, Japanese Patent Publication No. 4454067), and oxadiazole compounds (described in US Patent No. 4212970). For example, see paragraphs 0500 to 0547 of Japanese Unexamined Patent Publication No. 2012-208494.

[0152] Acylphosphine oxide compounds or oxime compounds are also preferred as polymerization initiators.

[0153] For example, commercially available BASF Japan Corporation's IRGACURE 810 (compound name: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) can be used as an oxime compound. Commercially available products such as IRGACURE OXE01 (BASF Corporation), IRGACURE OXE02 (BASF Corporation), TR-PBG-304 (Changzhou Qiangli Electronic New Materials Co., Ltd.), Adeka Arkles NCI-831, Adeka Arkles NCI-930 (ADEKA Corporation), and Adeka Arkles NCI-831 (ADEKA Corporation) can also be used as oxime compounds.

[0154] Polymerization initiators can be used in single-agent or in combination of two or more.

[0155] The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 5% by mass, relative to the content of the polymerizable liquid crystal compound.

[0156] (Cross-linking agent)

[0157] The liquid crystal composition may also contain a crosslinking agent to improve the strength and durability of the cured film. As a crosslinking agent, a crosslinking agent that cures through ultraviolet light, heat, or moisture can be appropriately used.

[0158] There are no particular limitations on the crosslinking agent; it can be appropriately selected according to the purpose. Examples of crosslinking agents include, for instance, polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl (meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-dihydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds with oxazoline groups on the side chains; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. Furthermore, known catalysts can be used depending on the reactivity of the crosslinking agent, which can improve not only film strength and durability but also productivity. These can be used alone or in combination of two or more.

[0159] The content of the crosslinking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass. By setting the content of the crosslinking agent to 3% by mass or more, the effect of increasing the crosslinking density can be obtained, and by setting the content of the crosslinking agent to 20% by mass or less, the stability of the cholesterol-type liquid crystal layer can be prevented from decreasing.

[0160] In addition, "(meth)acrylate" is used to mean "one or both of acrylate and methacrylate".

[0161] (Orientation control agent)

[0162] Orientation control agents that help stabilize or rapidly form planar orientation of the liquid crystal layer can also be added to the liquid crystal composition. Examples of orientation control agents include fluoro(meth)acrylate polymers described in paragraphs

[0018] to

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

[0031] to

[0034] of Japanese Patent Application Publication No. 2012-203237, and compounds described in Japanese Patent Application Publication No. 2013-113913.

[0163] Furthermore, as an orientation control agent, it can be used alone or in combination with two or more.

[0164] The amount of the orientation control agent added to the liquid crystal composition is preferably 0.01 to 10% by mass relative to the total mass of the polymerizable liquid crystal compound, more preferably 0.01 to 5% by mass, and particularly preferably 0.02 to 1% by mass.

[0165] (Other additives)

[0166] In addition, the liquid crystal composition may also contain at least one additive selected from various additives such as surfactants and polymerizable monomers used to adjust the surface tension of the coating to achieve uniform thickness. Furthermore, as needed, polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, color materials, and metal oxide particles may be further added to the liquid crystal composition without reducing optical performance.

[0167] Cholesterol-type liquid crystal layers can be formed as follows: a liquid crystal composition formed by dissolving a polymerizable liquid crystal compound, a polymerization initiator, a chiral auxiliary agent as needed, and a surfactant in a solvent is coated onto a support or alignment layer, dried to obtain a coating film, and the coating film is irradiated with active light to polymerize the cholesterol-type liquid crystal composition, thereby forming a cholesterol-type liquid crystal layer in which cholesterol regularity is fixed.

[0168] (solvent)

[0169] There are no particular restrictions on the solvents used in the preparation of liquid crystal compositions, and they can be appropriately selected according to the purpose, but organic solvents are preferred.

[0170] There are no particular limitations on organic solvents; they can be appropriately selected according to the purpose. Examples include ketones, haloalkanes, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These can be used alone or in combination of two or more. Among these, ketones are particularly preferred when considering the environmental impact.

[0171] (Coating, Orientation, Polymerization)

[0172] There are no particular limitations on the coating method of the liquid crystal composition onto the support and alignment layer, etc., and it can be appropriately selected according to the purpose. Examples of coating methods include wire rod coating, screen coating, extrusion coating, direct gravure coating, reverse gravure coating, mold coating, spin coating, dip coating, spray coating, and slide coating. Alternatively, it can be carried out by transferring the liquid crystal composition separately coated onto the support.

[0173] The liquid crystal molecules are oriented by heating the coated liquid crystal composition. The heating temperature is preferably below 200°C, more preferably below 130°C. This orientation process yields an optical thin film in which the polymeric liquid crystal compound is twisted and oriented in a direction substantially perpendicular to the film surface, such that it has a helical axis.

[0174] The liquid crystal composition can be cured by further polymerizing the oriented liquid crystal compound. Polymerization can be either thermal polymerization or photopolymerization using light irradiation, but photopolymerization is preferred. Ultraviolet light is preferably used for light irradiation. The irradiation energy is preferably 20 mJ / cm². 2 ~50J / cm 2 More preferably 100–1,500 mJ / cm 2 .

[0175] To promote photopolymerization, light irradiation can also be performed under heating conditions or a nitrogen atmosphere. The preferred wavelength of the irradiated ultraviolet light is 350–430 nm. From a stability perspective, a higher polymerization rate is better, preferably 70% or higher, and more preferably 80% or higher. The polymerization rate can be determined by measuring the infrared absorption spectrum to determine the proportion of polymerizable functional groups consumed.

[0176] <Other Layers>

[0177] In addition to the linearly polarized light reflecting layer 12 and polarization light conversion layer 11 described above, the reflective film 10 of the present invention may also include other layers as needed.

[0178] The other layers are preferably transparent in the visible light region.

[0179] Furthermore, the other layers are preferably of low birefringence. Low birefringence means that, within the wavelength range in which the reflective film 10 of the windshield of the present invention exhibits reflection, the frontal phase difference is less than 10 nm. This frontal phase difference is preferably less than 5 nm.

[0180] Other layers include the support, orientation layer, and adhesive layer.

[0181] (Support structure)

[0182] The support can also be used as a substrate when forming the linearly polarized light reflective layer and / or polarization conversion layer. The support used to form the linearly polarized light reflective layer and / or polarization conversion layer can also be a temporary support that is peeled off after the linearly polarized light reflective layer and / or polarization conversion layer has been formed. Therefore, the finished reflective film and windshield may not contain a support. Furthermore, if the support is included in the finished reflective film or windshield instead of being a temporary support peeled off, the support is preferably transparent in the visible light region.

[0183] There are no restrictions on the material of the support. Examples of supports include polyesters such as polyethylene terephthalate (PET), polycarbonate, acrylic resins, epoxy resins, polyurethanes, polyamides, polyolefins, cellulose derivatives, and silicone plastic films. In addition to the aforementioned plastic films, glass can also be used as a temporary support.

[0184] The thickness of the support should be around 5.0 to 1000 μm, preferably 10 to 250 μm, and more preferably 15 to 90 μm.

[0185] (Orientation layer)

[0186] The reflective film 10 may also include an alignment layer used to align the liquid crystal compound during the formation of the polarization conversion layer 11 as a lower layer on which the liquid crystal composition is coated.

[0187] Orientation layers can be formed through methods such as triboelectric treatment of organic compounds (resins such as polyimide, polyvinyl alcohol, polyester, polyarylate, polyamide-imide, polyether-imide, polyamide, and modified polyamide), oblique evaporation of inorganic compounds, formation of microgrooved layers, and accumulation of organic compounds (e.g., ω-trisanoic acid, dioctadecylmethylammonium chloride, and methyl stearate) using the Langmuir-Brønsted process (LB film). Alternatively, layers that generate orientation functions through the application of an electric field, a magnetic field, or light irradiation can also be used as orientation layers.

[0188] For example, the liquid crystal composition is preferably coated onto the rubbed surface after the alignment layer, which is made of polymer, has undergone a rubbing treatment. The rubbing treatment can be carried out by rubbing the surface of the polymer layer with paper or cloth in a certain direction.

[0189] Alternatively, the liquid crystal composition can be coated onto the surface of the support or onto the surface of the support after a friction treatment, without setting an alignment layer. When a temporary support is used to form the liquid crystal layer, the alignment layer can also be peeled off together with the temporary support and does not become a layer constituting the reflective element.

[0190] The thickness of the orientation layer is preferably 0.01 to 5.0 μm, and more preferably 0.05 to 2.0 μm.

[0191] (Adhesive layer)

[0192] The reflective film 10 may also have an adhesive layer if needed to improve the adhesion between the layers.

[0193] In the example of the reflective film 10, if an adhesive layer is provided, the adhesive layer can be provided between the linearly polarized light reflective layer 12 and the polarization light conversion layer 11.

[0194] The adhesive layer can be formed using an adhesive.

[0195] From the perspective of curing methods, adhesives can be categorized into hot-melt, thermosetting, light-curing, reaction-curing, and pressure-sensitive adhesives that do not require curing. As materials, various compounds can be used, including acrylate-based, urethane-based, urethane-acrylate-based, epoxy-based, epoxy-acrylate-based, polyolefin-based, modified olefin-based, polypropylene-based, ethylene vinyl alcohol-based, vinyl chloride-based, chloroprene rubber-based, cyanoacrylate-based, polyamide-based, polyimide-based, polystyrene-based, and polyvinyl butyral-based compounds. From the perspective of workability and productivity, light-curing is preferred as a curing method. From the perspective of optical transparency and heat resistance, acrylate-based, urethane-acrylate-based, and epoxy-acrylate-based materials are preferred.

[0196] The adhesive layer can also be formed using adhesives such as high-transparency adhesive transfer tape (OCA tape). As for high-transparency adhesive transfer tapes, commercially available products for image display devices, especially those for the surface of the image display section of image display devices, are acceptable. Examples of commercially available products include adhesive sheets (PD-S1, etc.) manufactured by Panac Corporation and MHM series adhesive sheets manufactured by Nichiei Chemical Co., Ltd.

[0197] There is no limitation on the thickness of the adhesive layer. The thickness of the adhesive layer formed using an adhesive is preferably 0.5–10 μm, more preferably 1.0–5.0 μm. Furthermore, the thickness of the adhesive layer formed using a high-transparency adhesive transfer tape (adhesive) is preferably 10–50 μm, more preferably 15–30 μm. To mitigate uneven color in the reflective film, a uniform thickness is preferred.

[0198] The windshield and head-up display (HUD) having the reflective film of the present invention will now be described.

[0199] [windshield]

[0200] Using the reflective film of the present invention, a windshield with a projected image display function can be provided.

[0201] A windshield refers to the general window glass and windshield of vehicles such as automobiles and trams, airplanes, ships, motorcycles, and amusement facilities. Windshields are preferably used as the front windshield or windshield located at the front of the vehicle's direction of travel.

[0202] There is no limitation on the visible light transmittance of the windshield, but a high visible light transmittance is preferred. The visible light transmittance of the windshield is preferably 70% or more, more preferably over 70%, further preferably over 75%, and particularly preferably over 80%.

[0203] The aforementioned visible light transmittance is preferably satisfied at any location on the windshield, and particularly preferably satisfied at the location where the reflective film is present. As described above, because the reflective film of the present invention has high visible light transmittance, it can be configured to satisfy the aforementioned visible light transmittance regardless of the type of glass commonly used in the windshield.

[0204] There are no restrictions on the shape of the windshield; it is appropriately determined based on the object on which the windshield is installed. A windshield can be, for example, flat or a three-dimensional shape with curved surfaces such as concave or convex. In a windshield shaped for a particular vehicle, the surface that is typically used in the upward direction, the observer's side, the driver's side, and the interior side can be specifically designated as the visual recognition side.

[0205] The thickness of the reflective film in the windshield can be uniform or non-uniform. For example, it can have a wedge-shaped cross-section, as described in Japanese Patent Publication No. 2011-505330, where the thickness of the reflective film is non-uniform, but it is preferable that the thickness of the reflective film is uniform.

[0206] When the reflective film of the present invention is disposed on the outer surface of the glass plate of the windshield, the linearly polarized light reflective film can be disposed inside the vehicle (on the incident side of the projected image) or outside the vehicle, but it is preferred to be disposed inside the vehicle.

[0207] Furthermore, the reflective film of the present invention has lower scratch resistance compared to glass. Therefore, in the case where the windshield is a laminated glass structure, it is more preferable to place the reflective film between the two panes of glass constituting the laminated glass in order to protect the reflective film.

[0208] As described above, a reflective film is a component used to display a projected image by reflecting the projected image. Therefore, the reflective film can be positioned so that the projected image from a projector or the like can be displayed in a visually recognizable manner.

[0209] That is, the reflective film of the present invention functions as a combiner in a HUD. In a HUD, a combiner is an optical component capable of displaying an image projected from a projector in a visually recognizable manner, and capable of simultaneously observing information such as scenery located on the opposite side of the incident surface of the projected light when viewing the combiner from the incident surface of the projected image. In other words, the combiner functions as an optical path combiner, displaying external light and the light from the projected image by coinciding.

[0210] The reflective film can be applied to the entire surface of the windshield, or it can be applied to a portion of the windshield in the surface direction, but it is preferred to apply it to a portion of the windshield.

[0211] When the reflective film is installed on part of the windshield, it can be installed anywhere on the windshield. However, when used as a HUD, it is preferable to install it in a position where the virtual image appears easily visible to observers such as the driver. For example, the position of the reflective film on the windshield can be determined based on the relationship between the position of the driver's seat and the position of the projector in a vehicle equipped with a HUD.

[0212] The reflective film can be a flat plane without any curves, or it can have a curved surface. Alternatively, the reflective film can have a concave or convex shape as a whole, in order to magnify or reduce the projected image.

[0213] Laminated glass

[0214] The windshield can also have a laminated glass structure. The windshield of the present invention is a laminated glass, with the above-described reflective film of the present invention between the first glass plate and the second glass plate.

[0215] The windshield can also be a structure in which a reflective film is disposed between the first glass panel and the second glass panel. However, the windshield is preferably a structure in which an interlayer film (intermediate film sheet) is disposed between at least one of the first glass panel and the reflective film and between the reflective film and the second glass panel.

[0216] In the windshield, as an example, the first glass panel is disposed on the side opposite to the visual recognition side of the image in the HUD (outer side of the vehicle), and the second glass panel is disposed on the visual recognition side (inner side of the vehicle). Furthermore, in the windshield of the present invention, the terms "first" and "second" in the first and second glass panels have no technical significance; they are simply provided for easy distinction between the two glass panels. Therefore, it is also possible for the first glass panel to be on the inner side of the vehicle and the second glass panel to be on the outer side of the vehicle.

[0217] The first and second glass plates can be made of glass commonly used in windshields. For example, glass plates with visible light transmittance of 73% or 76% or less, such as high-insulation green glass, can also be used. Even when using glass plates with low visible light transmittance, it is possible to produce a windshield with visible light transmittance of 70% or more at the location of the reflective film by using the reflective film of the present invention.

[0218] Furthermore, when the first glass panel and the second glass panel are curved glass, it is preferable to sequentially stack a linearly polarized light reflective layer, a polarized light conversion layer, and the first curved glass on the convex surface of the second curved glass, which serves as the interior side of the vehicle.

[0219] There are no particular restrictions on the thickness of the glass plate, which can be approximately 0.5 to 5.0 mm, preferably 1.0 to 3.0 mm, and more preferably 2.0 to 2.3 mm. The first and second glass plates can be made of the same material or have different thicknesses.

[0220] Windshields with a laminated glass structure can be manufactured using known laminated glass manufacturing methods.

[0221] Generally, it can be manufactured by the following method: after clamping the interlayer film for laminated glass between two glass plates, repeat the heat treatment and pressure treatment (using rubber rollers, etc.) multiple times, and finally, use an autoclave or the like for heat treatment under pressure.

[0222] As an example, a windshield with a structure of laminated glass having a reflective film and an interlayer film can be manufactured by the above-described method of manufacturing laminated glass after the reflective film is formed on the surface of the glass plate, or it can be manufactured by the above-described method of manufacturing laminated glass using an interlayer film including the above-described reflective film.

[0223] When a reflective film is formed on the surface of a glass plate, the glass plate on which the reflective film is applied can be either a first glass plate or a second glass plate. In this case, the reflective film is, for example, adhered to the glass plate using an adhesive.

[0224] (Intermediate membrane)

[0225] As the interlayer (interlayer film), any known interlayer used as an interlayer (intermediate layer) 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 chlorinated resins can be used. The aforementioned resin is preferably the main component of the interlayer. Furthermore, the main component refers to a component that accounts for 50% or more by mass of the interlayer.

[0226] Of the above-mentioned resins, polyvinyl butyral and ethylene-vinyl acetate copolymers are preferred, and polyvinyl butyral is more preferred. The resin is preferably a synthetic resin.

[0227] Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol with butyral. The preferred lower limit of the degree of acetalization of the aforementioned 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%.

[0228] Polyvinyl alcohol is usually obtained by saponifying polyvinyl acetate, typically using polyvinyl alcohol with a saponification degree of 80–99.8 mol%.

[0229] Furthermore, the preferred lower limit for the degree of polymerization of polyvinyl alcohol is 200, and the preferred upper limit is 3000. If the degree of polymerization of polyvinyl alcohol is 200 or higher, the penetration resistance of the obtained laminated glass is not easily reduced; if it is below 3000, the resin film has good formability and its rigidity is not too high, resulting in good processability. A more preferred lower limit is 500, and a more preferred upper limit is 2000.

[0230] (Intermediate film including the reflective film)

[0231] The interlayer for laminated glass containing a reflective film can be formed by laminating the reflective film to the surface of the aforementioned interlayer film. Alternatively, the reflective film can be sandwiched between two of the aforementioned interlayer films. The two interlayer films can be the same or different, but are preferably the same.

[0232] The lamination of the reflective film and the interlayer can be performed using known lamination methods, but pressing is preferred. Pressing is preferably performed under conditions of heat and pressure to prevent the laminate and interlayer from peeling off after processing.

[0233] To ensure stable pressing, the surface temperature of the interlayer film on the bonding side is preferably 50–130°C, more preferably 70–100°C.

[0234] It is preferable to apply pressure during the pressing process. There are no restrictions on the pressure conditions, but it is preferred to be below 2.0 kg / cm². 2 (below 196 kPa), more preferably 0.5–1.8 kg / cm² 2 (49~176kPa), further preferably 0.5~1.5kg / cm 2 (49~147kPa).

[0235] Alternatively, when the reflective film has a support, the support can be peeled off simultaneously with, after, or before pressing. That is, the reflective film adhered to the intermediate film obtained after pressing may also be without a support.

[0236] An example of a method for manufacturing an intermediate film including a reflective film includes:

[0237] (1) In the first step, the reflective film is bonded to the surface of the first intermediate film to obtain a first laminate; and

[0238] (2) Second step: attach the second intermediate film to the side of the reflective film in the first laminate that is opposite to the side to which the first intermediate film is attached.

[0239] For example, in the first step, the reflective film is bonded to the first intermediate film without the support being aligned with it. Next, the support is peeled off from the reflective film. Then, in the second step, the second intermediate film is bonded to the surface where the support has been peeled off. This allows the manufacture of an intermediate film containing a reflective film without a support. Furthermore, by using this intermediate film containing the reflective film, laminated glass with a reflective film without a support can be easily manufactured.

[0240] In order to ensure stable peeling of the support without damage, the temperature of the support when peeling it off from the reflective film is preferably 40°C or higher, more preferably 40 to 60°C.

[0241] [HUD (Head-Up Display System)]

[0242] A windshield can be used as a component of a HUD. A projector is preferably included in the HUD.

[0243] Projector

[0244] A "projector" is a "device for projecting light or an image," including a "device for projecting a drawn image," and emitting projection light carrying the displayed image. In the HUD of this invention, the projector emits projection light of p-polarized light.

[0245] In a HUD, the projector is configured to project p-polarized light carrying the image to be displayed onto a reflective film in the windshield at an angle of incidence.

[0246] In a HUD, preferably, the projector includes a drawing device that reflects and displays a virtual image of an image (real image) drawn on a small intermediate image screen via a combiner.

[0247] The projector can be any known projector used for HUDs, as long as it can emit p-polarized projection light. Furthermore, it is preferable that the imaging distance of the virtual image, i.e., the imaging position of the virtual image, is variable.

[0248] Methods for changing the imaging distance of the virtual image of a projector include, for example, moving the image generation surface (screen) (see Japanese Patent Application Publication No. 2017-21302), switching between multiple optical paths with different optical path lengths (see WO2015 / 190157), changing the optical path length by inserting and / or moving a mirror, changing the focal length by using a group of lenses as an imaging lens, moving the projector 22, switching between multiple projectors with different imaging distances of the virtual image, and using a variable focus lens (see WO2010 / 116912).

[0249] In addition, the projector can be a projector whose imaging distance of the virtual image can be continuously changed, or a projector whose imaging distance of the virtual image can be switched at multiple points, such as two or three points.

[0250] Preferably, the imaging distances of at least two virtual images in the projected light formed by the projector differ by more than 1 meter. Therefore, when the projector is one that can continuously change the imaging distance of the virtual images, it is preferable that the imaging distance of the virtual images can be changed by more than 1 meter. By using such a projector, it is preferable that appropriate responses can be made even when the distance of the driver's line of sight is significantly different, such as when driving at normal speed on a general road and driving at high speed on a highway.

[0251] (Drawing equipment)

[0252] A drawing device can be a device that displays images itself, or it can be a device that emits light capable of drawing images.

[0253] In a rendering device, light from a light source is adjusted using rendering methods such as a light modulator, a laser brightness modulation unit, or a light deflection unit for rendering. A rendering device refers to a device that includes a light source and, depending on the rendering method, includes a light modulator, a laser brightness modulation unit, or a light deflection unit for rendering.

[0254] (light source)

[0255] There are no restrictions on the light source; known light sources used in projectors, drawing equipment, and displays, such as LEDs (light-emitting diodes), organic light-emitting diodes (OLEDs), discharge tubes, and laser light sources, can be used.

[0256] Among these, LEDs are preferred, and particularly preferred, because LEDs and discharge tubes are suitable light sources for drawing devices that emit linearly polarized light. This is because the emission wavelength of LEDs is not continuous in the visible light region, making them suitable for combination with a combiner that uses a linearly polarized light reflective layer that exhibits selective reflectivity within a specific wavelength range.

[0257] (Drawing method)

[0258] There are no particular restrictions on the drawing method; it can be selected based on the light source used, etc.

[0259] Examples of drawing methods include those using fluorescent display tubes, liquid crystal displays (LCDs), liquid crystal on silicon (LCOSs), digital light processing (DLP), and laser scanning. Drawing can also be done using fluorescent display tubes integrated with the light source. LCDs are preferred as a drawing method.

[0260] In LCD and LCOS modes, light of each color is modulated and combined by a light modulator before being emitted from the projection lens.

[0261] The DLP method uses a DMD (Digital Micromirror Device) display system, which uses micromirrors with a certain number of pixels to draw, and light is emitted from a projection lens.

[0262] The scanning method involves scanning light across a screen and creating an image using the afterimage of the eye. For example, see Japanese Patent Application Publication Nos. 7-270711 and 2013-228674. In laser scanning, various colors of laser light, such as red, green, and blue, are modulated in brightness and then focused into a single beam by a beam combining optical system or a focusing lens. This beam is then scanned by a light deflection unit and drawn onto an intermediate image screen, as described later.

[0263] In scanning methods, for example, the brightness modulation of different colored lasers such as red, green, and blue light can be performed directly as changes in the intensity of the light source, or it can be done through an external modulator. Examples of light deflection units include galvanometer mirrors, combinations of galvanometer mirrors and multifaceted mirrors, and MEMS (Micro Electro Mechanical Systems), with MEMS being preferred. Examples of scanning methods include random scanning and grating scanning, but grating scanning is preferred. In grating scanning, for example, the laser can be driven at a resonant frequency in the horizontal direction and driven with a sawtooth wave in the vertical direction. Since scanning methods do not require projection lenses, miniaturization of the device is easier.

[0264] The light emitted from the drawing device can be linearly polarized light or natural light (unpolarized light).

[0265] In drawing devices using LCD or LCOS methods, and those using laser light sources, the emitted light is essentially linearly polarized. When the emitted light is linearly polarized and includes multiple wavelengths (colors), it is preferable that the polarization directions (transmission axis directions) of the multiple wavelengths are the same. Some commercially available drawing devices exhibit non-uniform polarization directions within the wavelength ranges of red, green, and blue light emitted (see Japanese Patent Application Laid-Open No. 2000-221449). Specifically, examples are known where the polarization direction of green light is orthogonal to the polarization directions of red and blue light.

[0266] Furthermore, in the HUD of the present invention, as described above, the projected light emitted by the projector is p-polarized light.

[0267] (The middle part resembles a screen)

[0268] As described above, the drawing device can also use an intermediate image screen. An "intermediate image screen" is a screen used to draw images. That is, when the light emitted from the drawing device is not yet visually recognizable as an image, the drawing device uses that light to form a visually recognizable image on the intermediate image screen. The image drawn on the intermediate image screen can be projected onto a combiner by light passing through the intermediate image screen, or it can be reflected from the intermediate image screen and projected onto the combiner.

[0269] Examples of intermediate image screens include scattering films, microlens arrays, and rear projection screens. When using plastic materials as intermediate image screens, if the screen is birefringent, the polarization plane and intensity of the polarized light incident on the screen will be disordered. This can easily lead to color inhomogeneity in the combiner (reflective film). However, by using a phase difference film with a specified phase difference, this problem of color inhomogeneity can be reduced.

[0270] As an intermediate image screen, it is preferable to have the function of diffusing and transmitting incident light. This is because it enables the magnified display of projected images. For example, a screen composed of a microlens array can be cited as such an intermediate image screen. Microlenses for HUDs are described, for example, in Japanese Patent Application Publication Nos. 2012-226303, 2010-145745, and 2007-523369.

[0271] Projectors may also include reflectors that adjust the optical path of the projected light generated by the drawing device.

[0272] For HUDs that use windshields as reflective films, see Japanese Patent Application Publication No. 2-141720, Japanese Patent Application Publication No. 10-96874, Japanese Patent Application Publication No. 2003-98470, US Patent No. 5013134, and Japanese Patent Application Publication No. 2006-512622, etc.

[0273] Windshields are particularly useful for HUDs used in conjunction with projectors that employ light sources such as lasers, LEDs, and OLEDs (organic light-emitting diodes) that emit light at wavelengths discontinuous in the visible light region. This is because the center wavelength of selective reflection from the cholesterol-type liquid crystal layer can be adjusted according to each emission wavelength. Additionally, they can be used for projection onto displays that show light polarization, such as LCDs (liquid crystal displays).

[0274] <Projected light (incident light)>

[0275] The incident light is preferably incident at an angle of 45° to 70° relative to the normal of the reflective film. The Brewster angle of the interface between glass with a refractive index of about 1.51 and air with a refractive index of 1 is about 56°. By incident p-polarized light within the above angle range, the surface of the windshield on the visual recognition side reflects less light relative to the selective reflective layer of the incident light used for projected image display, enabling image display with minimal ghosting.

[0276] The aforementioned angle is preferably 50° to 65°. At this point, 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 of the selective reflective layer on the incident side of the projected light.

[0277] The incident light can also enter from any direction, such as above, below, left, or right, of the windshield, as long as it corresponds to the direction of visual perception. For example, a structure in which the light enters from the downward direction during use at the tilted incident angle described above is preferred.

[0278] In addition, the reflective film on the windshield only needs to be configured to reflect incident p-polarized light.

[0279] As described above, the projected light in the HUD of the present invention is p-polarized light that vibrates in a direction parallel to the incident plane when displaying the projected image.

[0280] When the projector's emitted light is not linearly polarized, p-polarized light can be formed by providing a linearly polarized film (polarizer) on the projector's emitted light side, or by using known methods such as a linearly polarized film in the optical path from the projector to the windshield. In this case, the component that sets the non-linearly polarized projected light to p-polarized light is also considered as a component constituting the projector in the HUD of the present invention.

[0281] As described above, for projectors where the polarization direction of the emitted light is not uniform within the wavelength range 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 within the wavelength range of all colors.

[0282] As mentioned above, a HUD (projector) can also be a projection system that allows the virtual image to be projected in a variable position. By allowing the virtual image to be projected in a variable position, the driver can more comfortably and conveniently visually identify the virtual image.

[0283] The virtual image imaging position is the position where the virtual image can be visually recognized by the driver of the vehicle, such as a position that is usually more than 1000mm in front of the windshield as observed by the driver.

[0284] If, as described in Japanese Patent Application Publication No. 2011-505330, the glass is non-uniform (wedge-shaped) in the reflective film, then the angle of the wedge needs to be changed when the virtual image imaging position is altered. Therefore, for example, as described in Japanese Patent Application Publication No. 2017-15902, it is necessary to virtually respond to changes in the virtual image imaging position by locally changing the angle of the wedge and altering the projection position.

[0285] However, in the HUD of the present invention that uses the windshield of the present invention and utilizes p-polarized light as described above, since it is not necessary to use wedge-shaped glass and the thickness of the glass can be made uniform in the reflective film, a projection system that allows the virtual image imaging position to be variable can be appropriately adopted.

[0286] Next, refer to Figure 4 and Figure 5 Let's explain HUD in more detail.

[0287] Figure 4 This is a schematic diagram illustrating an example of a head-up display having a reflective film according to an embodiment of the present invention. Figure 5 This is a schematic diagram illustrating an example of a windshield having a reflective film according to an embodiment of the present invention.

[0288] The HUD20 includes a projector 22 and a windshield 24, and is used, for example, in vehicles such as passenger cars. Furthermore, the constituent elements of the HUD20 are as described above.

[0289] In HUD20, such as Figure 5 As shown in the conceptual diagram, the windshield 24 has a first glass plate 28 as a first glass plate, a second glass plate 30 as a second glass plate, a reflective film 10, an interlayer film 36, and an adhesive layer 38.

[0290] The reflective film 10 is Figure 1 The reflective film 10 shown has a selective reflective layer formed by alternating layers of optically anisotropic and isotropic layers. In the HUD 20, the left and right directions of the windshield 24 are aligned with... Figure 2 The reflective film 10 shown is configured with its transmission axis aligned. Furthermore, in the windshield (HUD) of the present invention, the reflective film may also have a support.

[0291] The vertical direction Y of the windshield 24 corresponds to the vertical direction of the vehicle on which the windshield 24 is mounted, and is the direction with the ground side as the lower side and the opposite side as the upper side. Furthermore, when the windshield 24 is mounted on a vehicle, it is sometimes mounted at an angle for structural or design convenience; however, in this case, the vertical direction Y becomes the direction along the surface 25 of the windshield 24. Surface 25 refers to the outer surface side of the vehicle.

[0292] Projector 22 is as described above. Projector 22 can be any projector capable of emitting projection light carrying p-polarized light that will display an image; known projectors for HUDs can be used. Furthermore, it is preferable that the imaging distance of the virtual image, i.e., the imaging position of the virtual image, is variable in projector 22.

[0293] In HUD20, projector 22 projects p-polarized light onto windshield 24 (second glass plate 30). By setting the projected light projected onto windshield 24 by projector 22 to p-polarized light, the reflection of the projected light by the second glass plate 30 and the first glass plate 28 of windshield 24 is greatly reduced, and undesirable conditions such as ghosting can be suppressed.

[0294] Preferably, the projector 22 projects p-polarized light onto the windshield at a Brewster angle. This eliminates reflections of the projected light onto the second glass plate 30 and the first glass plate 28, enabling a clearer image display.

[0295] The windshield 24 is a so-called laminated glass, having an interlayer 36, a reflective film 10, and an adhesive layer 38 between the first glass plate 28 and the second glass plate 30.

[0296] The projection light emitted from the projector 22 enters from the surface 30a of the second glass plate 30. The reflective film 10 reflects p-polarized light. As described above, the direction of the linearly polarized light reflected by the reflective film is set to reflect p-polarized light.

[0297] The reflective film 10 is bonded to the first glass plate 28 via the intermediate film 36 and 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.

[0298] In this invention, the first glass plate 28 and the second glass plate 30 of the windshield 24 are preferably arranged substantially parallel to each other.

[0299] Both the first glass plate 28 and the second glass plate 30 are known glass (glass plates) used for windshields of vehicles, etc. Therefore, the forming materials, thickness, and shape can be the same as those of known glass used for windshields. Figure 5 The first glass plate 28 and the second glass plate 30 shown are both flat, but not limited to this. They can also be partially curved or the entire surface can be curved.

[0300] The interlayer 36 is a film that prevents glass from penetrating into the vehicle and scattering in the event of an accident, and further serves as a film that bonds the reflective film 10 and the first glass panel 28. The interlayer 36 can be a known interlayer used in laminated glass windshields. Examples of materials forming the interlayer 36 include polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, chlorinated resins, and polyurethane.

[0301] Furthermore, there are no restrictions on the thickness of the interlayer 36; it can be set to the same thickness as the interlayer of a known windshield and the corresponding forming material.

[0302] The adhesive layer 38 is, for example, a layer made of a coating-type adhesive. The reflective film 10 is bonded to the second glass plate 30 via the adhesive layer 38. Alternatively, in the windshield of the present invention, the reflective film 10 may be bonded to the second glass plate 30 via an interlayer film instead of the adhesive layer 38. Furthermore, when the reflective film 10 is small, it may also be bonded to the second glass plate 30 via the interlayer film 36, which bonds the first glass plate 28 and the reflective film 10.

[0303] There are no limitations on the adhesive layer 38. As long as the required transparency for the windshield 24 is ensured and the reflective film 10 and glass are bonded with the required adhesive strength, an adhesive layer composed of various known coating-type adhesives can be used. The adhesive layer 38 can also use the same film as the intermediate film 36 such as PVB. Alternatively, the adhesive layer 38 can use acrylic adhesives, etc. Furthermore, as shown below, the adhesive layer 38 can also use the same adhesive layer as described above.

[0304] The adhesive layer 38 may be an adhesive layer formed of adhesive in the same way as the adhesive layer described above.

[0305] From the perspective of curing methods, adhesives can be categorized into hot-melt, thermosetting, light-curing, reaction-curing, and pressure-sensitive adhesives that do not require curing. Furthermore, regardless of the type, adhesives can utilize compounds such as acrylate-based, urethane-based, urethane-acrylate-based, epoxy-based, epoxy-acrylate-based, polyolefin-based, modified olefin-based, polypropylene-based, ethylene-vinyl alcohol-based, vinyl chloride-based, chloroprene rubber-based, cyanoacrylate-based, polyamide-based, polyimide-based, polystyrene-based, and polyvinyl butyral-based compounds as materials.

[0306] From the perspective of workability and productivity, light-curing is preferred as the curing method. From the perspective of optical transparency and heat resistance, the preferred materials are acrylate-based, urethane acrylate-based, and epoxy acrylate-based materials.

[0307] The adhesive layer 38 can also be formed using a high-transparency adhesive transfer tape (OCA tape). As a high-transparency adhesive transfer tape, commercially available products for image display devices, especially those for the surface of the image display section of an image display device, can be used. Examples of commercially available products include adhesive sheets (PD-S1, etc.) manufactured by Panac Co., Ltd., and adhesive sheets from the MHM series manufactured by Nichiei Chemical Co., Ltd.

[0308] There are no restrictions on the thickness of the adhesive layer 38. Therefore, the thickness can be appropriately set to obtain sufficient adhesive force, depending on the forming material of the adhesive layer 38.

[0309] Here, if the adhesive layer 38 is too thick, it may be impossible to bond the reflective film 10 to the first glass plate 28 or the second glass plate 30 while maintaining sufficient planarity. Taking this into consideration, the thickness of the adhesive layer 38 is preferably 0.1 to 800 μm, more preferably 0.5 to 400 μm.

[0310] Furthermore, the windshield 24 has an adhesive layer 38 between the reflective film 10 and the second glass plate 30, and an interlayer film 36 is used to bond the reflective film 10 and the first glass plate 28, but it is not limited to this. That is, it is also possible to have an adhesive layer between the reflective film 10 and the first glass plate 28, and an interlayer film between the reflective film 10 and the second glass plate 30.

[0311] Alternatively, the windshield 24 may be a structure without the intermediate film 36, but an adhesive layer 38 is used in the bonding of the reflective film 10 to the first glass plate 28 and the bonding of the reflective film 10 to the second glass plate 30.

[0312] In HUD20, the windshield 24 has the following structure: a reflective film 10 is provided between the first glass plate 28 and the second glass plate 30, the reflective film 10 is bonded to the second glass plate 30 by an adhesive layer 38, and the reflective film 10 is bonded to the first glass plate 28 by an intermediate film 36.

[0313] like Figure 4 As shown, in HUD20, the observer of the image, i.e. the driver D, observes the virtual image of the projected image formed by the projector 22, which is projected by the projector 22 and reflected by the windshield 24.

[0314] In a typical HUD, the projected image is reflected by the windshield, and the reflected light is observed. Here, the typical windshield is laminated glass, consisting of an inner surface and an outer surface. Therefore, in a HUD, there is a problem where the driver sees a ghosting effect due to the reflected light from the two glass panes.

[0315] To address this issue, in typical HUDs, the cross-sectional shape of the windshield (intermediate film) is wedge-shaped so that the reflections from the inner and outer surfaces of the glass overlap, thus eliminating the ghosting effect.

[0316] However, as mentioned above, in a wedge-shaped windshield, for example, when the imaging distance of the virtual image is changed to accommodate the difference in the driver's line of sight during normal driving with a closer line of sight and during high-speed driving with a farther line of sight, the angle of the wedge shape of the windshield does not match, and the image observed by the driver becomes a ghost image.

[0317] In contrast, in the HUD 20 of this invention, the projector 22 projects p-polarized light, and the windshield 24 has a reflective film 10 for reflecting p-polarized light between the first glass plate 28 and the second glass plate 30. The driver D observes the reflected light formed by the reflective film 10. In this structure, the reflection of the projected light from the projector 22 is mainly due to the reflection from the reflective film 10, thus making it virtually impossible to produce ghosting.

[0318] Therefore, in the HUD20 of which the reflective film 10 of the present invention is used in the windshield 24, it is not necessary to set the cross-sectional shape of the windshield 24 (intermediate film 36) to be wedge-shaped. Therefore, even if the imaging distance of the virtual image is changed, no ghosting will occur.

[0319] The present invention is essentially constructed as described above. The reflective film, windshield, and head-up display (HUD) system of the present invention have been described in detail above, but the present invention is not limited to the embodiments described above. Various modifications or alterations can be made without departing from the spirit of the present invention.

[0320] [Example]

[0321] The features of the present invention are further illustrated below with examples. The materials, reagents, quantities and proportions of substances, and operations shown in the following examples may be appropriately modified without departing from the spirit of the invention. Therefore, the scope of the present invention is not limited to the following examples.

[0322] <Fabrication of a Linearly Polarized Light Reflective Layer>

[0323] Based on the method described in Japanese Patent Application Publication No. 9-506837, a linearly polarized light reflective layer is fabricated as follows.

[0324] Using ethylene glycol as the diol, a copolyester of 2,6-poly(ethylene naphthalate) (PEN) and naphthalate 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 confirmed to be approximately 1.86, and the refractive index relative to the transverse axis was 1.64; the refractive index of the coPEN film was approximately 1.64.

[0325] Next, PEN and coPEN are simultaneously extruded using a 25-slot supply block fitted with a standard extrusion die, thereby forming alternating layers of PEN and coPEN with film thicknesses of 4 as shown in Table 1(1) below. Then, by repeating the same operation, alternating layers of PEN and coPEN with thicknesses of 4 and 8 as shown in Table 1(2) to (3) are formed sequentially, thereby creating a laminate consisting of a total of 16 layers. A coPEN film with a thickness of 10 μm is further extruded, and these laminates are stretched at approximately 150°C with a stretch ratio of 5:1.

[0326] [Table 1]

[0327] Table 1

[0328]

[0329] Next, the stretched laminate was heat-treated in an air oven at approximately 230°C for 30 seconds to fabricate a linearly polarized light reflective layer. The thickness of the fabricated linearly polarized light reflective layer was approximately 12 μm. The reflectance spectrum of the linearly polarized light reflective layer was measured using a spectrophotometer (manufactured by Nippon Spectrophotometer Co., Ltd., V-670), and a broad reflectance spectrum with a reflectance of approximately 20% was obtained in the reflectance band of 450 nm to 700 nm.

[0330] <Preparation of Coating Solution>

[0331] (Coating solution for forming polarization conversion layer A)

[0332] Mix the following components to prepare a coating solution for forming polarization conversion layer A with the following composition.

[0333]

[0334] [Chemical Formula 1]

[0335] Mixture 1

[0336]

[0337] [Chemical Formula 2]

[0338] Orientation control agent 1

[0339]

[0340] [Chemical Formula 3]

[0341] Orientation control agent 2

[0342]

[0343] (Coating solution for forming polarization conversion layer B)

[0344] Mix the following components to prepare a coating solution for forming polarization conversion layer B with the following composition.

[0345]

[0346] The amount of the dextrorotatory chiral additive LC756 in the coating solution for forming the polarization conversion layer B was adjusted to prepare a coating solution for forming the polarization conversion layer, such that the desired selective reflection center wavelength λ was obtained when forming a cholesterol-type liquid crystal layer. The selective reflection center wavelength λ was determined by forming a 3 μm thick monolayer of cholesterol-type liquid crystal layer on a temporary support and by FTIR (PerkinElmer, Spectrum Two) measurement.

[0347] The film thickness *d* of a helical structure can be represented by "the pitch *P* of the helical structure × the number of pitches". As mentioned above, the pitch *P* of the helical structure refers to the length of one pitch in the helical structure; a helical liquid crystal compound rotated 360° constitutes one pitch. Furthermore, in cholesteric liquid crystal layers, the selective reflection center wavelength *λ* coincides with "the length of one pitch *P* × the average in-plane refractive index *n*" (λ = P × *n*). Therefore, the pitch *P* becomes "the selective reflection center wavelength *λ* / the average in-plane refractive index *n*" (P = λ / n).

[0348] Therefore, a coating solution for forming polarization conversion layer B is prepared such that, in the case of forming a cholesterol-type liquid crystal layer, the reflection center wavelength λ is selected as the desired wavelength. In the formation of polarization conversion layer B, as described later, this coating solution for forming polarization conversion layer B is applied to the desired film thickness to form polarization conversion layer B and the pitch number is determined.

[0349] In Example 9, the pitch of the spiral structure of the polarization conversion layer B was adjusted to 0.25, the film thickness was 1.1 μm, and the reflection center wavelength λ was selected as 6864 nm.

[0350] [Example 1]

[0351] A polarization conversion layer A is formed by using a linearly polarized light reflective layer as a support and then forming the following alignment film on the support.

[0352] <Formation of Orientation Film>

[0353] On the linearly polarized light reflective layer, a wire bar coater was used at a rate of 24 mL / m. 2 Apply the coating solution for forming an orientation film as shown below and dry it with warm air at 100°C for 120 seconds.

[0354]

[0355] (Modified polyvinyl alcohol)

[0356] [Chemical Formula 6]

[0357]

[0358] The formed coating is rotated -30° clockwise from the long side of the support (refer to...). Figure 2 Friction treatment was performed (artificial fiber 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) to form an orientation film.

[0359] <Fabrication of Polarization Conversion Layer A>

[0360] After applying a coating liquid for forming polarization conversion layer A using wire rods to the surface of the alignment film on the support, it is allowed to dry.

[0361] Next, it was placed on a heating plate at 50°C in an environment with an oxygen concentration below 1000ppm, using an electrodeless lamp, the "D bulb" (60mW / cm²), manufactured by Fusion UVSystems. 2 Irradiate with ultraviolet light for 6 seconds to fix the liquid crystal phase. This forms a phase difference layer (polarization conversion layer A) whose thickness is divisible by the desired frontal phase difference, i.e., the desired frontal delay. Thus, a reflective film having a linearly polarized light reflecting layer and polarization conversion layer A is fabricated.

[0362] The frontal delay of the fabricated phase retardation layer was measured using AxoScan, and the result was 100 nm (Example 1).

[0363] [Comparative Example 1]

[0364] Except for not forming the polarization conversion layer A, the reflective film is fabricated in the same manner as in Example 1. That is, the linearly polarized light reflective layer monomer is used as the reflective film.

[0365] [Examples 2-8, Comparative Examples 2 and 3]

[0366] As shown in Table 2, the frontal retardation of the polarization conversion layer A and the angle between the direction of the slow axis and the direction of the transmission axis of the linearly polarized light reflecting layer were changed. Otherwise, the reflective film was fabricated in the same manner as in Example 1. Furthermore, the frontal retardation was adjusted by changing the film thickness of the polarization conversion layer compared to Example 1.

[0367] [Example 9]

[0368] A linearly polarized light reflecting layer with an oriented film is used as a support to form a polarization conversion layer B.

[0369] Friction treatment is applied to one side of the support along the long side of the support (artificial fiber 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).

[0370] After applying a polarization conversion layer B coating solution using a wire rod to the rubbed surface of the support, it is allowed to dry. Next, it is placed on a heating plate at 50°C in an environment with an oxygen concentration below 1000 ppm, and tested using an electrodeless lamp, a "D bulb" (60 mW / cm²), manufactured by Fusion UV Systems. 2 Irradiate with ultraviolet light for 6 seconds to fix the liquid crystal phase. This forms a polarization conversion layer B with a thickness equal to the desired value. Thus, a reflective film having a linearly polarized light reflecting layer and the polarization conversion layer B is fabricated.

[0371] [Comparative Examples 4-6]

[0372] By appropriately changing the amount of chiral additive and coating thickness of the coating liquid used to form polarization conversion layer B, and adjusting it to the pitch number and film thickness shown in Table 2, the polarization conversion layer B is formed in the same manner as in Example 9 to create a reflective film.

[0373] <Fabrication of Laminated Glass>

[0374] Laminated glass with the reflective films prepared above is manufactured as follows.

[0375] The obtained reflective film is cut into dimensions of 250mm (short side, vertical) × 280mm (long side, horizontal).

[0376] Prepare a glass plate (made of central glass, FL2, with a visible light transmittance of 90%) with a length of 300mm and a width of 300mm and a thickness of 2mm.

[0377] A PVB film, 0.76 mm thick and cut to the same size by Sekisui Chemicals, is placed on the glass plate as an intermediate film. A sheet-like linearly polarizing reflective film is then placed on the intermediate film, with the slow axis direction aligned with the longitudinal direction.

[0378] The same intermediate film and glass plate as described above are set on the linear polarizing light reflective film.

[0379] After holding the laminate at 90°C and 10 kPa (0.1 atm) for one hour, it was heated in an autoclave (made by Kurihara Manufacturing Co., Ltd.) at 115°C and 1.3 MPa (13 atm) for 20 minutes to remove air bubbles and obtain laminated glass.

[0380] [Echoes of the previous sentence]

[0381] The reflectance of P-polarized light was measured with and without a black PET film, and ghosting was evaluated based on the difference in brightness.

[0382] (Determination of reflectivity of P-polarized light)

[0383] P-polarized light is incident on the linearly polarized reflective layer side of the laminated glass at a 65° angle relative to the glass's normal direction. The reflectance spectrum of the positively reflected light (located on the side of the incident plane opposite to the normal direction, at a 65° angle relative to the normal direction) is measured using a spectrophotometer (manufactured by Nippon Spectrophotometer Co., Ltd., V-670). The long side of the reflective film is aligned parallel to the transmission axis of the incident P-polarized light on the spectrophotometer. Then, the glass is rotated 20 degrees clockwise around the transmission axis.

[0384] According to JIS R3106, the reflectance of the projected image is calculated by multiplying the reflectance by a coefficient corresponding to the visual sensitivity and the emission spectrum of the D65 light source in every 10 nm wavelength range of 380–780 nm, and is used as an evaluation of brightness.

[0385] Next, a black PET film containing a light absorber was adhered to the back side of the laminated glass, and the aforementioned P-polarized light reflectance was measured. This measurement eliminates the influence of the brightness of the light reflected (projected image) from the glass surface by adhering the black PET film, allowing for the measurement of the brightness of the light reflected by the reflective film.

[0386] Based on the measurement results, the proportion of the brightness of the light reflected (projected image) on the glass surface that becomes a double image is calculated using the following formula, and evaluated according to the following evaluation criteria.

[0387] Ghosting = ((Brightness - Brightness (Black PET Sticker)) / Brightness) × 100 [%)

[0388] Evaluation Criteria for Ghosting

[0389] ·AA below 7%

[0390] • A percentage exceeding 7% but below 10% (ghosting is difficult to see)

[0391] • B exceeds 10% (ghosting can be seen)

[0392] [Evaluation of the adaptability of polarized sunglasses]

[0393] S-polarized light is incident on the glass surface of the laminated glass opposite to the linearly polarized light reflector at a direction of 65° relative to the normal direction of the glass. The transmittance spectrum of the transmitted light is measured from the opposite side of the incident surface of the laminated glass using a spectrophotometer (manufactured by Japan Spectrophotometer Co., Ltd., V-670).

[0394] At this point, a linear polarizer is positioned on the light-receiving part of the spectrophotometer, so that the vertical direction of the windshield is parallel to the transmission axis of the incident p-polarized light from the spectrophotometer. Then, the glass is rotated 20 degrees counterclockwise around the transmission axis.

[0395] According to JIS R3106, the visible light transmittance is calculated by multiplying the wavelength in the range of 380–780 nm by a coefficient corresponding to visual sensitivity and the emission spectrum of a D65 light source for each 10 nm interval. This transmittance is then used to evaluate the suitability of polarized sunglasses. The evaluation of the suitability of polarized sunglasses is conducted according to the following evaluation criteria.

[0396] Evaluation Criteria for the Adaptability of Polarized Sunglasses

[0397] AA is less than 2%

[0398] • A 2% or more to less than 3%

[0399] • B 3% or more to less than 5%

[0400] ·C 5% or more

[0401] The results are shown in Table 2. Furthermore, in Table 2, the layer obtained by immobilizing the helical orientation structure of the liquid crystal compound as polarization conversion layer B is labeled as a twisted layer. Additionally, the value of (1560×y) / x is labeled as value (iii).

[0402] [Table 2]

[0403] Table 2

[0404]

[0405] As shown in Table 2, it can be seen that the embodiments of the present invention achieved better results in terms of ghosting compared to the comparative examples. Furthermore, it can be seen that the embodiments of the present invention also achieved good results in terms of adaptability to polarized sunglasses.

[0406] As can be seen from the comparison of Examples 1 to 8, it is preferred that the front retardation of the phase difference layer, which is the polarization conversion layer A, is 50nm to 120nm and the angle β is within 20°.

[0407] As can be seen from the comparison between Example 9 and Comparative Examples 4 to 6, when the polarization conversion layer is a layer obtained by immobilizing the helical orientation structure of the liquid crystal compound, the pitch number x of the helical orientation structure and the film thickness y (in μm) of the polarization conversion layer satisfy all the above-mentioned relationships (i) to (iii), thereby improving the adaptability to ghosting and polarized sunglasses.

[0408] Based on the above results, the effects of the present invention are clear.

[0409] [Industry availability]

[0410] It can be appropriately used in vehicle-mounted head-up display (HUD) systems, etc.

[0411] Symbol Explanation

[0412] 10. Reflective film

[0413] 11 Polarization conversion layer

[0414] 12 Linearly polarized light reflector layer

[0415] 12a Optical Anisotropy Layer

[0416] 12b Isotropic layer

[0417] 20. Head-up Display (HUD) System

[0418] 22 Projectors

[0419] 24 Windshield

[0420] 25, 30a surfaces

[0421] 28 First Glass Plate

[0422] 30 Second glass plate

[0423] 36 Intermediate membrane

[0424] 38 Adhesive layer

[0425] Driver D

[0426] Y (Up / Down Direction)

Claims

1. A reflection film for a head-up display system for a vehicle, having: a linearly polarized light reflection layer in which an optically anisotropic layer and an isotropic layer are laminated, and a polarized light conversion layer, which is disposed in the order of the linearly polarized light reflection layer, the polarized light conversion layer from a visual recognition side when applied to the head-up display system for the vehicle, the polarized light conversion layer is a layer which converts an s-polarized light component of light which becomes elliptically polarized light from linearly polarized light upon oblique incidence to the linearly polarized light reflection layer into a p-polarized light component, the polarized light conversion layer satisfies the following condition (A): (A) the polarized light conversion layer is a phase difference layer, a front surface retardation at a wavelength of 550 nm is 35 nm to 180 nm, and from the linearly polarized light reflection layer side of the reflection film, an angle of a direction of a slow axis on the acute angle side from a direction of a transmission axis of the linearly polarized light reflection layer is represented as + for clockwise and - for counterclockwise, and an absolute value of the angle of the direction of the slow axis on the acute angle side from the direction of the transmission axis of the linearly polarized light reflection layer is within 30°.

2. The reflection film according to claim 1, wherein the polarized light conversion layer is a phase difference layer, a front surface retardation at a wavelength of 550 nm is 70 nm to 120 nm, and an absolute value of an angle of a direction of a slow axis on the acute angle side from a direction of a transmission axis of the linearly polarized light reflection layer is within 15°.

3. The reflection film according to claim 1 or 2, wherein a number of laminations of the optically anisotropic layer and the isotropic layer of the linearly polarized light reflection layer is 10 layers to 60 layers.

4. A windshield having: the reflection film according to any one of claims 1 to 3; and a first curved glass and a second curved glass which sandwich the reflection film, the linearly polarized light reflection layer, the polarized light conversion layer are sequentially laminated from a convex side of the second curved glass, the first curved glass.

5. A head-up display system having: the windshield according to claim 4; and a projector which irradiates p-polarized light of a projection image light from the second curved glass side of the windshield. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images