Reflective film, windshield and heads-up display system

Abstract

The present application provides a kind of reflecting film, windshield and head-up display system, the reflecting film has high visible light transmittance and can improve the brightness of display image, the transparency of appearance tone is good.The reflecting film has selective reflection layer, the selective reflection layer has the cholesteric liquid crystal layer formed by fixed cholesteric liquid crystal phase, in each range of the range of wavelength 400nm above and less than 500nm and the range of wavelength 500nm above and less than 600nm, the maximum value of natural light reflectance is 10%~25%, the difference between the maximum maximum value and the minimum minimum value is 3% or more, the added value of wavelength band of the region higher than the average of maximum value and minimum value is 20nm~80nm, in the range of wavelength 600nm above and 800nm below, the maximum value of natural light reflectance is 10%~25%, the added value of wavelength band of the region higher than the average of maximum value and minimum value is 120nm or more.

Description

Technical Field

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

[0002] Currently, there is a so-called head-up display or head-up display system that projects images onto the windshield of a vehicle or other object to provide drivers or other users with various information such as maps, speed, and vehicle status.

[0003] In a head-up display (HUD) system, the driver and others can observe a virtual image of the various information projected onto the windshield. The virtual image is projected further outward and forward than the windshield. Typically, the virtual image is projected at least 1000mm further outward and further outward than the windshield. Therefore, the driver can obtain this information without significantly shifting their gaze while looking ahead. Thus, using a HUD system allows for the acquisition of various information and can be expected to result in safer driving.

[0004] Head-up display systems can be constructed by forming a reflective film on the windshield using a semi-reflective film. Various semi-reflective films suitable for use in head-up display systems have been proposed.

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

[0006] Patent Document 1 describes a light-reflecting film that is assembled into a windshield to form a head-up display system. The windshield (assembler) that forms the head-up display system requires high visible light transmittance.

[0007] Previous technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2016 / 056617 Summary of the Invention

[0010] The technical problem to be solved by the invention

[0011] In this context, from the perspective of transmittance and design considerations, as required by laws and regulations, the in-vehicle head-up display system must have a transparent appearance regardless of the viewing angle.

[0012] In order to maintain a legally permissible transmittance of over 70% to make the appearance color close to transparent, the reflectivity has traditionally been reduced. However, if the reflectivity is reduced too much, the brightness of the displayed image (projected image) will decrease, resulting in poor visual recognition.

[0013] The objective of this invention is to provide a reflective film with high visible light transmittance, which can improve the brightness of the displayed image and has good transparency in appearance and tone, a windshield using the reflective film, and a head-up display system.

[0014] means for solving technical problems

[0015] [1] A reflective film having a selective reflective layer having a cholesterol-type liquid crystal layer formed by fixing a cholesterol-type liquid crystal phase.

[0016] The reflective layer is selected to satisfy all of the following necessary conditions (i) to (iii).

[0017] (i) In the range of wavelengths above 400 nm and below 500 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm.

[0018] (ii) In the range of wavelengths above 500 nm and below 600 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm.

[0019] (iii) In the range of wavelengths above 600 nm and below 800 nm, the maximum value of natural light reflectance is 10% to 25%, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is above 120 nm.

[0020] [2] According to the reflective film described in [1], the selective reflective layer has two or more cholesteric liquid crystal layers with different selective reflective center wavelengths.

[0021] Cholesterol-type liquid crystal layers are in contact with each other.

[0022] [3] According to the reflective film of [1] or [2], wherein the selective reflective layer comprises a cholesteric liquid crystal layer having two or more selective reflective center wavelengths.

[0023] [4] The reflective film according to any one of [1] to [3], wherein the total thickness of the reflective layer is selected to be 0.4 μm to 2.0 μm.

[0024] [5] The reflective film according to any one of [1] to [4] reflects linearly polarized light.

[0025] [6] The reflective film according to any one of [1] to [5] has a phase difference layer, a selective reflection layer and a polarization conversion layer in sequence.

[0026] [7] According to the reflective film described in [6], the polarization conversion layer is formed by fixing the helical orientation structure of the liquid crystal compound.

[0027] The pitch number x of the spiral orientation structure in the polarization conversion layer and the film thickness y (μm) of the polarization conversion layer satisfy all of the following equations (a) to (c).

[0028] 0.1≤x≤1.0···Equation (a)

[0029] 0.5≤y≤3.0···Equation (b)

[0030] 3000≤(1560×y) / x≤50000···Equation (c)

[0031] [8] A windshield having, in sequence, a first glass plate, a reflective film as described in any one of [1] to [7], and a second glass plate.

[0032] [9] According to the windshield described in [8], wherein the first glass panel and the second glass panel are curved glass.

[0033] A reflective film and a second glass plate are provided on the convex side of the first glass plate.

[0034]

[10] According to the windshield described in [9], the reflective film has a polarization conversion layer.

[0035] A polarization conversion layer and a selective reflection layer are sequentially arranged from the convex side of the first glass plate.

[0036]

[11] The windshield according to [9] or

[10] , wherein the reflective film has a phase retardation layer,

[0037] The phase retardation layer is positioned between the selective reflective layer and the second glass plate.

[0038] The frontal delay of the phase retardation layer at a wavelength of 550nm is 50nm to 160nm, and when the direction corresponding to the vertical direction above the surface of the first glass panel when the windshield is mounted on the vehicle is set to 0°, the angle of the slow axis is 10° to 50° or -50° to -10°.

[0039]

[12] The windshield according to any one of [9] to

[11] , wherein the reflective film has a transparent substrate,

[0040] A transparent substrate is disposed on the side of the second glass plate.

[0041]

[13] The windshield according to

[12] , wherein the transparent substrate contains an ultraviolet absorber.

[0042]

[14] The windshield according to any one of [8] to

[13] has an intermediate film between the first glass plate and the reflective film.

[0043]

[15] The windshield according to any one of [8] to

[14] has a heat-sealing layer between the reflective film and the second glass plate.

[0044]

[16] A head-up display system comprising: a windshield as described in any one of [9] to

[15] ; and

[0045] The projector shines a projected image onto the first glass panel of the windshield.

[0046]

[17] According to the head-up display system described in

[16] , the projector illuminates p-polarized projected image light.

[0047] Invention Effects

[0048] According to the present invention, a reflective film with high visible light transmittance, which can improve the brightness of the displayed image and has good transparency of appearance tone, a windshield, and a head-up display system can be provided. Attached Figure Description

[0049] Figure 1 This is a schematic diagram illustrating an example of the reflective film of the present invention.

[0050] Figure 2 It is a graph showing the relationship between wavelength and transmittance.

[0051] Figure 3 This is a schematic diagram illustrating an example of a windshield having the reflective film of the present invention.

[0052] Figure 4 It is a graph showing the relationship between wavelength and transmittance.

[0053] Figure 5This is a schematic diagram illustrating an example of a head-up display having the reflective film of the present invention. Detailed Implementation

[0054] Hereinafter, the reflective film, windshield, and head-up display system of the present invention will be described in detail with reference to the preferred embodiments shown in the accompanying drawings.

[0055] Furthermore, the figures described below are illustrative examples of the present invention, and the present invention is not limited to the figures shown below.

[0056] Additionally, the "~" sign used to indicate a range of values ​​includes the values ​​on either side. For example, ε1 being α1 to β1 means that the range of ε1 includes both α1 and β1. In mathematical notation, α1 ≤ ε1 ≤ β1.

[0057] Unless otherwise specified, "angles expressed in specific numerical values", "parallel", "perpendicular" and "orthogonal" angles include the error range that is generally allowed in the corresponding technical field.

[0058] Furthermore, "same" includes the error range that is usually allowed in the corresponding technical field, and "the entire surface" also includes the error range that is usually allowed in the corresponding technical field.

[0059] When referred to as "light," unless otherwise specified, it refers to visible light and natural light (unpolarized light). Visible light is the electromagnetic wave with wavelengths observable by the human eye, typically representing light in the wavelength range of 380–780 nm. Invisible light is light with wavelengths less than 380 nm or greater than 780 nm.

[0060] Furthermore, although not limited to this, the wavelength region of visible light in the 420–490 nm range is blue (B) light, the wavelength region of 495–570 nm range is green (G) light, and the wavelength region of 620–750 nm range is red (R) light.

[0061] "Visible light transmittance" refers to 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). Specifically, it is the transmittance calculated as follows: Using light source A, the transmittance at each wavelength within the range of 380–780 nm is measured with a spectrophotometer. The transmittance at each wavelength is then multiplied by a weighted average of the transmittance obtained from the wavelength distribution and wavelength intervals of the CIE (International Commission on Illumination) light adaptability standard for visibility.

[0062] When referred to simply as "reflected light" or "transmitted light," it is used to include both scattered and diffracted light.

[0063] p-polarized light refers to polarized light that vibrates in a direction parallel to the plane of incidence. The plane of incidence is a surface perpendicular to the reflecting surface (such as the surface of a windshield) and includes both the incident and reflected rays. The plane of vibration of the electric field vector of p-polarized light is parallel to the plane of incidence.

[0064] The frontal phase difference is measured using an AxoScan manufactured by Axometrics Inc. Unless otherwise specified, the measurement wavelength is set to 550 nm. The frontal phase difference can also be measured using a KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments) by incident light of wavelengths within the visible light range along the normal to the film. When selecting the measurement wavelength, the wavelength selection filter can be manually changed, or the measurement value can be converted using a program.

[0065] A "projection image" refers to an image projected based on light from the projector used, rather than an image based on the surrounding scenery such as what's in front of you. When viewed from the observer's perspective, a projection image can be observed as a virtual image floating in front of the reflective film on the windshield.

[0066] "Screen image" refers to an image displayed on a projector's drawing device or an image drawn on an intermediate image screen, etc., by a drawing device. An image is a real image, as opposed to a virtual image.

[0067] Both images and projected images can be monochrome, multi-color (two or more colors), or full-color.

[0068] [Reflective film]

[0069] The reflective film of the present invention has a selective reflective layer.

[0070] The selective reflective layer has a cholesterol-type liquid crystal layer formed by fixing a cholesterol-type liquid crystal phase.

[0071] The reflective layer is selected to satisfy all of the following necessary conditions (i) to (iii).

[0072] (i) In the range of wavelengths above 400 nm and below 500 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm.

[0073] (ii) In the range of wavelengths above 500 nm and below 600 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm.

[0074] (iii) In the range of wavelengths above 600 nm and below 800 nm, the maximum value of natural light reflectance is 10% to 25%, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is above 120 nm.

[0075] Figure 1 This is a schematic diagram illustrating an example of the reflective film of the present invention. Figure 1 The reflective film 10 shown has a polarization conversion layer 14, a selective reflection layer 11, a phase difference layer 16, and a transparent substrate 18 in sequence.

[0076] The selective reflective layer 11 comprises three cholesteric liquid crystal layers (12R, 12G, and 12B). The selective reflective center wavelengths of the three cholesteric liquid crystal layers are different from each other. In the example shown, the layers are, in sequence, cholesteric liquid crystal layer 12R, which has a selective reflective center wavelength in the red wavelength region; cholesteric liquid crystal layer 12G, which has a selective reflective center wavelength in the green wavelength region; and cholesteric liquid crystal layer 12B, which has a selective reflective center wavelength in the blue wavelength region. Furthermore, in the example shown, each cholesteric liquid crystal layer is in direct contact with any other cholesteric liquid crystal layer.

[0077] As is well known, a cholesterol-type liquid crystal layer is a layer formed by fixing a liquid crystal compound in a helical orientation of a cholesterol-type liquid crystal phase. It reflects light at a selectively reflected central wavelength corresponding to the pitch of the helical structure, while transmitting light in other wavelength regions. Furthermore, the cholesterol-type liquid crystal layer exhibits selective reflectivity for either circularly polarized light (left or right) at a specific wavelength.

[0078] Here, in this invention, the reflective layer is selected to satisfy all of the following necessary conditions (i) to (iii).

[0079] (i) In the range of wavelengths above 400 nm and below 500 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm.

[0080] (ii) In the range of wavelengths above 500 nm and below 600 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm.

[0081] (iii) In the range of wavelengths above 600 nm and below 800 nm, the maximum value of natural light reflectance is 10% to 25%, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is above 120 nm.

[0082] In a selective reflective layer with a cholesterol-type liquid crystal layer, the wavelength and reflectivity of the reflected light can be adjusted according to the selective reflective center wavelength and thickness (number of helical pitches) of the cholesterol-type liquid crystal layer. Figure 1 In the example shown, the reflection that satisfies the necessary condition (i) is achieved by the cholesterol-type liquid crystal layer 12B, which mainly reflects light in the blue wavelength region; the reflection that satisfies the necessary condition (ii) is achieved by the cholesterol-type liquid crystal layer 12G, which reflects light in the green wavelength region; and the reflection that satisfies the necessary condition (iii) is achieved by the cholesterol-type liquid crystal layer 12R, which reflects light in the red wavelength region.

[0083] Figure 2 Examples of natural light reflectance spectra that satisfy the above necessary conditions (i) to (iii) are shown. Figure 2 The graph shown is an example of the natural light reflectance spectrum of the reflective film of Example 1, which will be described later.

[0084] Figure 2 The graph shows that in the wavelength range of 400 nm to 500 nm, the natural light reflectance reaches its maximum value (maximum) near 480 nm, approximately 14.5%, falling within the range of 10% to 25%. Furthermore, in the same wavelength range, the natural light reflectance reaches its minimum value near 440 nm, approximately 9.5%. Therefore, the difference between the maximum and minimum values ​​of natural light reflectance is approximately 5%, exceeding 3%. Similarly, in the same wavelength range, the natural light reflectance reaches its minimum value near 440 nm, approximately 9.5%. Therefore, the average of the maximum and minimum values ​​of natural light reflectance is 12%. The wavelength bandwidths of the region where natural light reflectance exceeds this 12% are approximately 415 nm to 430 nm and 445 nm to 490 nm, with the sum of these bandwidths being approximately 60 nm, falling within the range of 20 nm to 80 nm.

[0085] therefore, Figure 2The spectrum shown in the curve satisfies the necessary condition (i).

[0086] Figure 2 The graph shows that in the wavelength range of 500 nm to 600 nm, the natural light reflectance reaches its maximum value (maximum) near 555 nm, with a value of approximately 15.5%, falling within the range of 10% to 25%. Furthermore, in the same wavelength range, the natural light reflectance reaches its minimum value near 505 nm, with a value of approximately 9%. Therefore, the difference between the maximum and minimum values ​​of natural light reflectance is approximately 6.5%, exceeding 3%. Similarly, in the same wavelength range, the natural light reflectance reaches its minimum value near 505 nm, with a value of approximately 9%. Therefore, the average of the maximum and minimum values ​​of natural light reflectance is 12.3%. The wavelength bandwidth of the region with natural light reflectance above this 12.3% is approximately 520 nm to 575 nm, and the sum of these wavelength bandwidths is approximately 55 nm, falling within the range of 20 nm to 80 nm.

[0087] therefore, Figure 2 The spectrum shown in the curve satisfies the necessary condition (ii).

[0088] Figure 2 The graph shows that in the spectral range above 600 nm and below 800 nm, the natural light reflectance reaches its maximum value (maximum) near 750 nm, at approximately 18.3%, falling within the range of 10% to 25%. Furthermore, in the same range, the natural light reflectance reaches its minimum value near 600 nm, at approximately 11.3%. Therefore, the average of the maximum and minimum natural light reflectance values ​​is 14.8%. The wavelength bandwidth of the region with natural light reflectance above this 14.8% is approximately 650 nm to 780 nm, and the sum of these wavelength bandwidths is approximately 130 nm, exceeding 120 nm.

[0089] therefore, Figure 2 The spectrum shown in the curve satisfies necessary condition (iii).

[0090] As mentioned above, in automotive head-up display systems, from a legal and regulatory perspective, and from a design standpoint, a transparent appearance is required regardless of the viewing angle. To maintain a legally mandated transmittance of over 70% to achieve a near-transparent (white) appearance, reducing reflectivity has been considered in the past. However, excessively reducing reflectivity decreases the brightness of the displayed image (projected image), leading to poorer visual clarity.

[0091] In contrast, the reflective film of the present invention improves tonal transparency by setting the maximum value of natural light reflectance at wavelengths of 500 nm and above to less than 600 nm within the range of 10% to 25%. To ensure the legally required 70% frontal transmittance, a reflectance around 550 nm, which is the visibility factor, is crucial. Therefore, by setting the maximum value of natural light reflectance at wavelengths of 500 nm and above to less than 600 nm to 25% or less, transmittance can be ensured. Furthermore, to improve brightness, a higher reflectance around 550 nm in the oblique direction (60° of incident angle) is required. The reflective film of the present invention, by satisfying a maximum natural light reflectance of 10% to 25% at wavelengths of 600 nm and above to less than 800 nm and a reflective band width of 120 nm or more, improves the frontal brightness of the displayed image and enhances tonal transparency when viewed from an oblique direction (60° of incident angle). Furthermore, if only wavelengths above 500 nm and below 600 nm are reflected, the reflected hue on the front side will become yellow to red. Therefore, the reflective film of the present invention, by setting the maximum value of natural light reflectance at wavelengths above 400 nm and below 500 nm to 10% to 25%, can improve the transparency of the hue when viewed from near the front side (incident angle 5°). Moreover, by setting the difference between the maximum and minimum values ​​of natural light reflectance in each band of wavelengths above 400 nm and below 500 nm and wavelengths above 500 nm and below 600 nm to 3% or more, and by setting the sum of the wavelength bandwidths of the regions higher than the average of the maximum and minimum values ​​of natural light reflectance to 20 nm to 80 nm (i.e., narrow band), wavelength regions with low reflectance can be formed in each band of wavelengths above 400 nm and below 500 nm and wavelengths above 500 nm and below 600 nm, thereby improving transmittance.

[0092] Based on these effects, the natural light transmittance of windshields made by sandwiching a reflective film with green glass can reach 70% or more (compared to 80% or more when sandwiched with transparent glass). Furthermore, the reflectivity of the displayed image relative to the wavelength of light can reach 25% or more, thereby improving the brightness of the displayed image. Additionally, the transparency of the color tone can be improved when viewed from all directions.

[0093] From the viewpoint of being able to improve both reflective hue and transmittance, the maximum value of natural light reflectance in the range of 400 nm and above but less than 500 nm is preferably 11% to 20%, more preferably 12% to 20%.

[0094] Similarly, from the viewpoint of being able to improve transmittance while improving reflective hue, the maximum value of natural light reflectance in the range of 500 nm and above but less than 600 nm is preferably 11% to 20%, more preferably 12% to 20%.

[0095] From the viewpoint of being able to improve the brightness of the displayed image while improving the reflected color tone, the maximum value of the natural light reflectance in the range of 600nm and above and 800nm ​​and below is preferably 15% to 23%, more preferably 16% to 23%.

[0096] From the viewpoint of being able to improve transmittance while improving reflective hue, the difference between the maximum and minimum values ​​of natural light reflectance in the range of 400 nm and 500 nm is preferably 4% or more and 20% or less, more preferably 4% or more and 12% or less.

[0097] Similarly, from the viewpoint of being able to improve transmittance while improving reflective hue, the difference between the maximum and minimum values ​​of natural light reflectance in the range of 500 nm and above and less than 600 nm is preferably 4% or more and 20% or less, more preferably 4% or more and 12% or less.

[0098] From the viewpoint of being able to improve transmittance while improving reflective hue, the wavelength bandwidth of the region where the average of the maximum and minimum reflectance values ​​of reflectance is above 400 nm and below 500 nm is preferably above 30 nm and below 78 nm, more preferably above 35 nm and below 75 nm.

[0099] Similarly, from the viewpoint of being able to improve transmittance while improving reflective hue, the wavelength bandwidth of the region where the average of the maximum and minimum reflectance values ​​of reflectance is above 500 nm and below 600 nm is preferably above 30 nm and below 78 nm, more preferably above 35 nm and below 75 nm.

[0100] Regarding the wavelength bandwidths in the range of 400 nm to 500 nm and in the range of 500 nm to 600 nm, a narrower bandwidth is more beneficial to transmittance. However, since the wavelength bandwidth in the range of 600 nm to 800 nm is relatively wide, if the wavelength bandwidths in the range of 400 nm to 500 nm and / or in the range of 500 nm to 600 nm are too narrow, the reflectance color tone may deteriorate. Therefore, the wavelength bandwidths in the range of 400 nm to 500 nm and in the range of 500 nm to 600 nm are preferably set within the aforementioned ranges.

[0101] Furthermore, for transmittance, the wavelength bandwidth in the range of 500nm and above but less than 600nm has a greater impact.

[0102] From the viewpoint of improving the front brightness of the displayed image while enhancing the reflective hue, the wavelength bandwidth of the region where the average of the maximum and minimum reflectance values ​​of reflectance is above 600 nm and below 800 nm is preferably above 120 nm and below 200 nm.

[0103] Here, as Figure 1 As shown, the selective reflective layer preferably has two or more cholesteric liquid crystal layers with different selective reflective center wavelengths. Furthermore, each cholesteric liquid crystal layer is preferably in direct contact with any other cholesteric liquid crystal layer. For example, in... Figure 1 In the example shown, a cholesterol-type liquid crystal layer 12R having a selective reflection center wavelength in the red wavelength region and a cholesterol-type liquid crystal layer 12G having a selective reflection center wavelength in the green wavelength region are in contact with each other, and a cholesterol-type liquid crystal layer 12G having a selective reflection center wavelength in the green wavelength region and a cholesterol-type liquid crystal layer 12B having a selective reflection center wavelength in the blue wavelength region are in contact with each other.

[0104] If the cholesteric liquid crystal layers are spaced apart, the interlayer thickness becomes too thick, making it difficult to achieve the interference effect of light reflected by each cholesteric liquid crystal layer. In contrast, by arranging the cholesteric liquid crystal layers in contact with each other, the wavelength bandwidth can be narrowed by utilizing the interference effect of light reflected by each cholesteric liquid crystal layer. In particular, if the thickness of each cholesteric liquid crystal layer is thinner than the wavelength of light (visible light 380nm–780nm), the interference effect becomes even more significant.

[0105] Furthermore, in this invention, when the reflective layer 11 is selected to have two or more cholesterol-type liquid crystal layers, each cholesterol-type liquid crystal layer is not limited to a structure in direct contact, but may also be a structure stacked via an adhesive layer or the like.

[0106] Here, each cholesterol-type liquid crystal layer only needs to have at least one selective reflection center wavelength, but it is also possible for at least one cholesterol-type liquid crystal layer to have two or more selective reflection center wavelengths. Cholesterol-type liquid crystal layers with two or more selective reflection center wavelengths are achieved by a helical structure in which the helical pitch varies in the thickness direction.

[0107] Furthermore, in the example shown, the selective reflective layer 11 is configured to have a structure with three cholesteric liquid crystal layers having different selective reflective center wavelengths, but it is not limited to this. The selective reflective layer 11 may also have one cholesteric liquid crystal layer, or it may have two or more cholesteric liquid crystal layers.

[0108] The total thickness of the reflective layer 11 is preferably 0.4 μm to 2.0 μm, more preferably 0.6 μm to 1.8 μm, and even more preferably 0.8 μm to 1.4 μm.

[0109] If the total thickness of the reflective layer 11 is too thin, its reflectivity to natural light will be too low, potentially failing to improve the brightness of the displayed image. On the other hand, if the total thickness of the reflective layer 11 is too thick, its transmittance may decrease.

[0110] Here, the reflective film of the present invention preferably reflects linearly polarized light. When the reflective film is assembled into a windshield as a head-up display unit, in order to suppress reflections on the windshield surface, the projected image light is preferably p-polarized light (i.e., linearly polarized light).

[0111] On the other hand, in this invention, the reflective layer is selected to have a cholesterol-type liquid crystal layer and to reflect circularly polarized light.

[0112] Therefore, the reflective film of the present invention preferably has a layer that converts linearly polarized light incident on the reflective film into circularly polarized light. Examples of layers that convert the polarization state of light include a polarization conversion layer and a phase difference layer.

[0113] The polarization conversion layer exhibits optical rotation and birefringence in response to visible light, and converts the polarization state of incident light. In this invention, the polarization conversion layer is composed of a layer of a birefringent material, such as a liquid crystal compound, oriented with a twist of less than 360°.

[0114] A phase retardation layer adds a phase difference (optical path difference) to two orthogonally polarized light components to convert the state of the incident polarized light. In this invention, the phase retardation layer is a layer made of birefringent materials such as liquid crystal compounds arranged in the same direction, and it does not have optical rotation.

[0115] By configuring the reflective film to have a polarization conversion layer or phase difference layer on the side where the light incident on the selective reflective layer is incident, it is possible to convert linearly polarized light incident on the reflective film into circularly polarized light. The selective reflective layer reflects the circularly polarized light, and the polarization conversion layer or phase difference layer converts the reflected circularly polarized light back into linearly polarized light for emission.

[0116] Here, in Figure 1 In the example shown, the reflective film 10 has a polarization conversion layer 14 on one side of the selective reflective layer 11 and a phase retardation layer 16 on the other side. As an example, when this reflective film 10 is assembled into a windshield, it is described later. Figure 3 As shown, the polarization conversion layer 14 is configured to serve as the first glass panel 28 side inside the vehicle, and the phase difference layer 16 serves as the second glass panel 30 side outside the vehicle.

[0117] In this case, the polarization conversion layer 14 has the function of converting the projected p-polarized light (linearly polarized light) into circularly polarized light reflected by the cholesteric liquid crystal layer of the selective reflective layer 11.

[0118] On the other hand, the retardation layer 16 has the function of optically compensating for light incident from the outside of the windshield. For example, the polarization state of s-polarized light incident from the outside of the windshield changes when it passes through the polarization conversion layer 14, resulting in the presence of p-polarized light components. Since polarized sunglasses block s-polarized light, these p-polarized light components will be transmitted through the polarized sunglasses. Therefore, the function of polarized sunglasses in blocking glare from reflected light, which is mainly composed of s-polarized light, is impaired, which can hinder driving. In contrast, by using the retardation layer 16 for optical compensation in a structure with the retardation layer 16, the applicability of polarized sunglasses can be improved.

[0119] In addition, Figure 3 In the example shown, the reflective film 10 is configured such that the polarization conversion layer 14 is the side of the first glass panel 28 on the inner side of the vehicle and the phase retardation layer 16 is the side of the second glass panel 30 on the outer side of the vehicle, but it is not limited to this configuration. The reflective film 10 may also be configured such that the polarization conversion layer 14 is the side of the second glass panel 30 on the outer side of the vehicle and the phase retardation layer 16 is the side of the first glass panel 28 on the inner side of the vehicle.

[0120] In this case, the phase difference layer 16 has the function of converting the projected p-polarized light (linearly polarized light) into circularly polarized light reflected by the cholesteric liquid crystal layer of the selective reflective layer 11.

[0121] On the other hand, the polarization conversion layer 14 has the function of optically compensating for light incident from the outside of the windshield. By using the polarization conversion layer 14 for optical compensation, the applicability of polarized sunglasses can be improved.

[0122] Furthermore, the reflective film of the present invention may also be a structure having polarization conversion layers on both sides of the selective reflective layer 11, or a structure having phase difference layers on both sides.

[0123] In this case, it is sufficient to configure the polarization conversion layer or phase difference layer disposed inside the vehicle to have the function of converting the projected p-polarized light (linearly polarized light) into circularly polarized light reflected by the cholesteric liquid crystal layer of the selective reflective layer 11.

[0124] On the other hand, it is sufficient to design a structure in which the polarization conversion layer or phase difference layer located on the outside of the vehicle has the function of optically compensating for light incident from the outside of the windshield.

[0125] The polarization conversion layer and phase difference layer will be described in detail later.

[0126] [windshield]

[0127] The windshield of the present invention is a windshield having a first glass plate, the above-mentioned reflective film and a second glass plate in sequence.

[0128] Windshields refer to ordinary window glass and windproof glass used in vehicles such as automobiles and trams, airplanes, ships, two-wheeled vehicles, and amusement rides. Windshields are preferably used as the front window and windproof glass located at the front of the vehicle in the direction of travel.

[0129] Figure 3 An example of a windshield is shown in the image.

[0130] Figure 3 The windshield 24 shown has a first glass plate 28, an intermediate film 36, a reflective film 10, a heat-sealing layer 38, and a second glass plate 30 in sequence.

[0131] exist Figure 3 In the middle, the reflective film 10 has the same characteristics as... Figure 1 The reflective film 10 shown has the same structure, with the polarization conversion layer 14 on the side of the first glass plate 28 and the phase difference layer 16 (transparent substrate 18) on the side of the second glass plate 30.

[0132] When the windshield of the present invention is used in a vehicle, curved glass is typically used as the first glass panel 28 and the second glass panel 30. In this case, if the first glass panel 28 is the inner side of the vehicle and the second glass panel 30 is the outer side of the vehicle, the first glass panel 28 is configured such that its convex side faces the second glass panel 30, and the second glass panel 30 is configured such that its concave side faces the first glass panel 28.

[0133] When the first glass plate 28 and the second glass plate 30 are curved glass, Figure 3 In the example shown, a polarization conversion layer 14 and a selective reflection layer 11 are sequentially arranged from the convex side of the first glass plate 28. Furthermore, a phase difference layer 16 is disposed between the selective reflection layer 11 and the second glass plate 30.

[0134] There is no limitation on the visible light transmittance of the windshield, but a higher transmittance is preferred. The visible light transmittance of the windshield is preferably 70% or more, more preferably more than 70%, further preferably 75% or more, and especially preferably 80% or more.

[0135] Preferably, the aforementioned visible light transmittance is satisfied at any location on the windshield, and particularly preferably at the location where the reflective film is present. As described above, the reflective film of the present invention has high visible light transmittance, thus satisfying the aforementioned visible light transmittance regardless of the type of glass commonly used for windshields.

[0136] As an example, Figure 4 The image shows a device held between two glass plates. Figure 2 The graph shows an example of the natural light reflectance spectrum of a windshield with a reflective film. This example is the windshield of Example 1.

[0137] like Figure 4 As shown, even when the reflective film of the present invention is held in place by thick glass, the unevenness of the natural light reflection spectrum of the reflective film will still remain.

[0138] There are no restrictions on the shape of the windshield; it can be appropriately determined according to the object on which the windshield is installed. The windshield can be, for example, flat or a three-dimensional shape with curved surfaces such as concave or convex surfaces. In a windshield molded into a windshield for a vehicle of application, the surfaces that are normally used in the upward direction, the observer's side, the driver's side, and the interior side of the vehicle can be defined.

[0139] In a windshield, the reflective film only needs to be installed on the part of the windshield where the projected image is displayed (the part where the projected image is reflected).

[0140] Furthermore, in a windshield, the reflective film can be a structure disposed between the glass panes of a laminated glass windshield, or it can be a structure disposed on the outer surface of the glass panes of the windshield.

[0141] When the reflective film of the present invention is disposed on the outer surface of the glass plate of the windshield, the reflective film can be disposed inside the vehicle (on the incident side of the projected image) or outside, but it is preferred to be disposed inside.

[0142] Furthermore, the scratch resistance of the reflective film of the present invention is lower than that of the glass plate. Therefore, in the case where the windshield is a laminated glass structure, in order to protect the reflective film, it is more preferable to place the reflective film between the two pieces of glass constituting the laminated glass.

[0143] As described above, the reflective film is a component used to display a projected image by reflecting the projected image. Therefore, the reflective film can be positioned to display the projected image projected from a projector or the like in a visually recognizable manner.

[0144] That is, the reflective film of the present invention functions as a combiner in a head-up display (hereinafter also referred to as a HUD). In a HUD, the combiner refers to an optical component that is capable of displaying an image projected from a projector in a visually recognizable manner, and when the combiner is viewed from the incident surface of the projected image, information such as scenery located on the surface opposite to the incident surface of the projected light can be viewed simultaneously. In other words, the combiner functions as an optical path combiner that overlaps and displays ambient light and the projected image.

[0145] The reflective film can be applied to the entire surface of the windshield, or it can be applied to a portion of the surface of the windshield, but it is preferred to apply it to a portion.

[0146] When the reflective film is installed on part of the windshield, it can be placed at any location on the windshield. However, when used as a HUD, it is preferable to display the virtual image in a position that is easily visible to an observer 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 in the vehicle equipped with the HUD and the position of the projector.

[0147] The reflective film can be a flat plane without a curved surface, or it can be curved. Furthermore, the reflective film can also have a concave or convex shape as a whole, and can magnify or reduce the projected image.

[0148] The following describes the constituent elements of the reflective film and windshield of the present invention.

[0149] <Selecting a Reflective Layer>

[0150] The reflective layer is selected to have a cholesterol-type liquid crystal layer, and the reflection satisfies the above-mentioned necessary conditions (i) to (iii).

[0151] [Cholesterol-type liquid crystal layer]

[0152] Cholesterol-type liquid crystal layer refers to a layer formed by fixing a cholesterol-type liquid crystal phase.

[0153] A cholesterol-type liquid crystal layer is simply a layer that can maintain the orientation of the liquid crystal compound, which 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 into a cholesterol-type liquid crystal phase after it has been oriented to that state, through ultraviolet irradiation and heating, to render it non-flowable and simultaneously change its orientation morphology to a state that will not change due to external fields or forces. Furthermore, in a cholesterol-type liquid crystal layer, it is sufficient that the optical properties of the cholesterol-type liquid crystal phase are maintained within the layer; the liquid crystal compound within the layer may no longer exhibit liquid crystal properties. For example, the polymerizable liquid crystal compound can be molecularized through a curing reaction, thereby losing its liquid crystal properties.

[0154] It is known that cholesterol-type liquid crystal phases selectively reflect circularly polarized light of either right-handed or left-handed rotation and selectively reflect circularly polarized light transmitted by the other rotation.

[0155] As films comprising a cholesteric liquid crystal phase exhibiting selective reflectivity to circularly polarized light, various films formed from compositions containing polymeric liquid crystal compounds are known in the past. Regarding cholesteric liquid crystal layers, these prior art techniques can be referenced.

[0156] The selective reflection center wavelength λ of a cholesterol-type liquid crystal layer depends on the pitch P (=helical period) 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. According to this formula, the selective reflection center wavelength can be adjusted by adjusting the value of n and / or the value of P.

[0157] In other words, the pitch P (one helical pitch) of a helical structure refers to the length of one turn of the helix along the helical axis, that is, the length along the helical axis when 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 is aligned with the thickness direction of the cholesterol-type liquid crystal layer.

[0158] As an example, the selective reflection center wavelength and half-width of a cholesterol-type liquid crystal layer can be determined as follows.

[0159] When measuring the reflectance spectrum of a cholesterol-type liquid crystal layer from the normal direction using a spectrophotometer (JASCO Corporation, V-670), a transmittance reduction peak can be observed in the selected reflectance band. Let λ be the wavelength of the shorter wavelength side of the two wavelengths representing the minimum transmittance and the intermediate (average) transmittance before the reduction. l (nm), where the wavelength value on the longer wavelength side is set to λ. h If the reflection center wavelength λ and half-width Δλ are (nm), then the selection of the reflection center wavelength λ and half-width Δλ can be expressed by the following formula.

[0160] λ=(λ l +λ h ) / 2, Δλ=(λ h -λ l )

[0161] The wavelength of the selected reflection center, as determined above, is approximately the same as 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.

[0162] In the head-up display system described later, by using it in a way that the light is incident at an angle onto the windshield, the reflectivity of the glass surface on the side where the projected light is incident can be reduced.

[0163] At this time, light is also incident obliquely on the cholesteric liquid crystal layer 11 that constitutes the reflective film 10. For example, light incident at an angle of 45° to 70° relative to the normal of the reflective film 10 in air with a refractive index of 1 is transmitted at an angle of about 26° to 36° to the cholesteric liquid crystal layer with a refractive index of about 1.61. In this case, the reflected wavelength is shifted to the shorter wavelength side.

[0164] When light passes through a cholesteric liquid crystal layer with a selective reflection center wavelength of wavelength λ at an angle θ2 relative to the normal direction of the cholesteric liquid crystal layer (the direction of the helical axis of the cholesteric liquid crystal layer), the selective reflection center wavelength is set to wavelength λ. d When, wavelength λ d It is expressed by the following formula.

[0165] λ d =λ×cosθ2

[0166] Therefore, for example, a cholesteric liquid crystal layer with a selective reflection center wavelength in the range of 650 to 780 nm when θ2 is 26° to 36° can reflect projected light in the range of 520 to 695 nm.

[0167] Because this wavelength range is a region with high visibility, it contributes significantly to the brightness of the projected image, resulting in a high-brightness projected image.

[0168] The helical pitch of a cholesterol-type liquid crystal phase depends on the type and concentration of the chiral reagent used with the polymerizable liquid crystal compound; therefore, the desired pitch can be obtained by adjusting these factors. Furthermore, methods for determining the helix direction and pitch can be found in "Introduction to Liquid Crystal Chemistry Experiments" (compiled by the Japan Liquid Crystal Society, published by Sigma Publishing in 2007, p. 46) and "Liquid Crystal Handbook" (Liquid Crystal Handbook Editorial Committee, Maruzen Junkudo Bookstores Co., Ltd., p. 196).

[0169] Each cholesterol-type liquid crystal layer uses a helix with a direction of rotation that is either right-handed or left-handed. The direction of rotation of the circularly polarized light reflected by the cholesterol-type liquid crystal layer (the direction of rotation of the circularly polarized light) is consistent with the direction of rotation of the helix.

[0170] In the case of multiple cholesterol-type liquid crystal layers with different selective reflection center wavelengths, the spiral directions of each cholesterol-type liquid crystal layer can be the same or include different spiral directions. However, it is preferable that the spiral directions of the multiple cholesterol-type liquid crystal layers are all the same.

[0171] Furthermore, when the reflective film 10 has multiple cholesteric liquid crystal layers as selective reflective layers 11, cholesteric liquid crystal layers exhibiting selective reflection in the same or repeating wavelength regions are preferably excluded. This is to avoid the transmittance in specific wavelength regions, for example, decreasing to less than 50%.

[0172] The half-width Δλ (nm) of the selective reflection band exhibiting selective reflection depends on the birefringence Δn of the liquid crystal compound and the aforementioned pitch P, and follows the relationship Δλ = Δn × P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. Δn can be adjusted by changing the type or mixing ratio of the polymerizable liquid crystal compound or by controlling the temperature during orientation fixation.

[0173] To form a cholesteric liquid crystal layer with the same selective reflection center wavelength, multiple cholesteric liquid crystal layers with the same pitch P and the same helical direction can be stacked. By stacking cholesteric liquid crystal layers with the same pitch P and the same helical direction, the selectivity of circularly polarized light at a specific wavelength can be improved.

[0174] In the selection of reflective layer 11, when multiple cholesteric liquid crystal layers are stacked, an adhesive or the like can be used to stack individually prepared cholesteric liquid crystal layers, or a liquid crystal composition containing polymerizable liquid crystal compounds or the like can be directly coated on the surface of the cholesteric liquid crystal layer formed by the method described later, and the alignment and fixing processes are repeatedly performed, but the latter method is preferred.

[0175] This is because, by directly forming the next cholesterol-type liquid crystal layer on the surface of the first-formed cholesterol-type liquid crystal layer, the orientation of the liquid crystal molecules on the air interface side of the first-formed cholesterol-type liquid crystal layer can be aligned with the orientation of the liquid crystal molecules on the lower side of the cholesterol-type liquid crystal layer formed thereon, thereby improving the polarization characteristics of the stack of cholesterol-type liquid crystal layers. Furthermore, interference unevenness that might arise due to uneven thickness of the adhesive layer cannot be observed.

[0176] The thickness of the cholesterol-type liquid crystal layer is preferably 0.5–10 μm, more preferably 1.0–8.0 μm, and even more preferably 1.5–6.0 μm.

[0177] (Method for fabricating cholesterol-type liquid crystal layers)

[0178] The following describes the materials and manufacturing methods for cholesterol-type liquid crystal layers.

[0179] Examples of materials used to form the aforementioned cholesterol-type liquid crystal layer include liquid crystal compositions containing polymerizable liquid crystal compounds and chiral reagents (optically active compounds). The aforementioned liquid crystal composition, which is further mixed with surfactants and polymerization initiators as needed and dissolved in a solvent, can be coated onto a support, an alignment layer, or a cholesterol-type liquid crystal layer that forms the bottom layer. After cholesterol-type alignment curing, the liquid crystal composition is cured to fix the layer, thereby forming a cholesterol-type liquid crystal layer.

[0180] (polymeric liquid crystal compound)

[0181] 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.

[0182] 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, azobenzene compounds, azo oxide compounds, cyanobiphenyl compounds, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexane compounds, cyano-substituted phenylpyrimidine compounds, alkoxy-substituted phenylpyrimidine compounds, phenyl dioxane compounds, 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.

[0183] Polymerizable liquid crystal compounds are obtained by incorporating polymeric groups into a liquid crystal compound. Examples of polymeric groups include unsaturated polymeric groups, epoxy groups, and aziridinyl groups, with unsaturated polymeric groups being preferred, and olefinic unsaturated polymeric groups being particularly preferred. Polymeric groups can be incorporated into the molecule of the liquid crystal compound by various methods. The number of polymeric groups in a polymerizable liquid crystal compound is preferably 1 to 6 per molecule, more preferably 1 to 3.

[0184] 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. 6-016616, Japanese Patent Application Publication No. 7-110,469, Japanese Patent Application Publication No. 11-080081, and Japanese Patent Application Publication No. 2001-328,973. Two or more polymerizable liquid crystal compounds can be used simultaneously. Using two or more polymerizable liquid crystal compounds simultaneously can lower the alignment temperature.

[0185] 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 mass of the solvent), more preferably 85 to 99.5% by mass, and particularly preferably 90 to 99% by mass.

[0186] To improve visible light transmittance, cholesterol-type liquid crystal layers can have low Δn. Low-Δn cholesterol-type liquid crystal layers can be formed using low-Δn polymerizable liquid crystal compounds. The following provides a detailed explanation of low-Δn polymerizable liquid crystal compounds.

[0187] (Low Δn polymerizability liquid crystal compounds)

[0188] By using low-Δn polymerizability liquid crystal compounds to form a cholesterol-type liquid crystal phase and using it as a fixed film, a narrow-band selective reflective layer can be obtained. Examples of low-Δn polymerizability liquid crystal compounds include those described in WO2015 / 115390, WO2015 / 147243, WO2016 / 035873, Japanese Patent Application Publication Nos. 2015-163596 and 2016-053149. For liquid crystal compositions providing a selective reflective layer with a small half-width, see also WO2016 / 047648.

[0189] The liquid crystal compound is preferably a polymeric compound represented by the following formula (I) as described in WO2016 / 047648.

[0190] [Chemical Formula 1]

[0191]

[0192] In formula (I), A represents a phenylene group that may have substituents or a trans-1,4-cyclohexylene group that may have substituents; L represents a single bond, a linking group selected from the group consisting of -CH2O-, -OCH2-, -(CH2)2OC(=O)-, -C(=O)O(CH2)2-, -C(=O)O-, -OC(=O)O-, -CH=CH-C(=O)O-, and -OC(=O)-CH=CH-; m represents an integer from 3 to 12; Sp 1 and Sp 2 Each independently represents a linking group selected from the group consisting of one or more -CH2- groups substituted with -O-, -S-, -NH-, -N(CH3)-, -C(=O)-, -OC(=O)- or -C(=O)O-, including straight-chain or branched alkylene groups having 1 to 20 carbon atoms. 1 and Q 2 Each of the following independently represents a hydrogen atom or a polymeric group selected from the group represented by formulas Q-1 to Q-5, wherein Q 1 and Q 2 Any one of them represents a polymerizable group.

[0193] [Chemical Formula 2]

[0194]

[0195] The phenylene in formula (I) is preferably 1,4-phenylene.

[0196] The substituents used when referring to phenylene and trans-1,4-cyclohexene as "potentially substituents" are not particularly limited. Examples include substituents selected from the group consisting of alkyl, cycloalkyl, alkoxy, alkyl ether, amide, amino, and halogen atoms, as well as groups composed of two or more of the aforementioned substituents. Furthermore, as an example of a substituent, -C(=O)-X (described later) can be cited. 3 -Sp 3 -Q 3 The substituents are indicated. Phenylidene and trans-1,4-cyclohexylene may have 1 to 4 substituents. When there are 2 or more substituents, the 2 or more substituents may be the same as or different from each other.

[0197] The alkyl group can be either straight-chain or branched. The number of carbon atoms in the alkyl group is preferably 1 to 30, more preferably 1 to 10, and even more preferably 1 to 6. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, 1,1-dimethylpropyl, n-hexyl, isohexyl, straight-chain or branched heptyl, octyl, nonyl, decyl, undecyl, or dodecyl. The above description of alkyl groups applies to alkoxy groups containing alkyl groups. Furthermore, specific examples of alkylene groups when referred to as alkylene groups include divalent groups obtained by removing any one hydrogen atom from the examples of alkyl groups described above. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine atoms.

[0198] The cycloalkyl group preferably has 3 to 20 carbon atoms, more preferably 5 or more, and more preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl.

[0199] The substituents that can be present in the phenylene and trans-1,4-cyclohexene groups are particularly preferably selected from alkyl, alkoxy, and -C(=O)-X groups. 3 -Sp 3 -Q 3 The substituents in the group. Where X 3 Indicates a single bond, -O-, -S-, or -N (Sp 4 -Q 4 )-, or to indicate the relationship with Q 3 and Sp 3 Nitrogen atoms that form a ring structure together. Sp 3 Sp 4Each of these groups independently represents a single bond and a linking group selected from the group consisting of one or more -CH2- groups substituted with -O-, -S-, -NH-, -N(CH3)-, -C(=O)-, -OC(=O)- or -C(=O)O- from straight-chain or branched alkylene groups having 1 to 20 carbon atoms.

[0200] Q 3 and Q 4 Each of the following independently represents a hydrogen atom, a cycloalkyl group, or one or more of the cycloalkyl groups whose -CH2- is substituted by -O-, -S-, -NH-, -N(CH3)-, -C(=O)-, -OC(=O)- or -C(=O)O-, or any polymerizable group selected from the group consisting of groups represented by formulas Q-1 to Q-5.

[0201] As a group in a cycloalkyl group, one or more -CH2- are substituted with -O-, -S-, -NH-, -N(CH3)-, -C(=O)-, -OC(=O)-, or -C(=O)O-. Specifically, examples include tetrahydrofuranyl, pyrrolylyl, imidazolidinyl, pyrazolyl, piperidinyl, piperazinyl, and morpholinyl. The substitution position is not particularly limited. Tetrahydrofuranyl is preferred, and 2-tetrahydrofuranyl is especially preferred.

[0202] In formula (I), L represents a single bond, selected from -CH2O- and -OCH-. 2- The linking group is from the group consisting of -(CH2)2OC(=O)-, -C(=O)O(CH2)2-, -C(=O)O-, -OC(=O)O-, -CH=CH-C(=O)O-, and -OC(=O)-CH=CH-. L is preferably -C(=O)O- or -OC(=O)-. The m-1 L groups can be the same or different from each other.

[0203] Sp 1 Sp 2 Sp represents, independently, a linking group selected from the group consisting of one or more -CH2- groups substituted with -O-, -S-, -NH-, -N(CH3)-, -C(=O)-, -OC(=O)- or -C(=O)O-, comprising straight-chain or branched alkylene groups having 1 to 20 carbon atoms. 1 and Sp 2The linking group is preferably a straight-chain alkylene group with 1 to 10 carbon atoms, which is independently and preferably bonded to two ends with a linking group selected from the group consisting of -O-, -OC(=O)- and -C(=O)O-, or a combination of one or more groups selected from the group consisting of -OC(=O)-, -C(=O)O-, -O- and straight-chain alkylene groups with 1 to 10 carbon atoms. It is more preferably a straight-chain alkylene group with 1 to 10 carbon atoms, which is bonded to two ends with -O-.

[0204] Q 1 and Q 2 Each independently represents a hydrogen atom or a polymeric group selected from the group represented by formulas Q-1 to Q-5 above, wherein Q 1 and Q 2 Any one of them represents a polymerizable group.

[0205] As a polymerizable group, acryloyl (formula Q-1) or methacryloyl (formula Q-2) are preferred.

[0206] In formula (I), m represents an integer from 3 to 12. m is preferably an integer from 3 to 9, more preferably an integer from 3 to 7, and even more preferably an integer from 3 to 5.

[0207] As A, the polymerizable compound represented by formula (I) preferably contains at least one substituted phenylene group and at least one substituted trans-1,4-cyclohexylene group. As A, the polymerizable compound represented by formula (I) preferably contains 1 to 4 substituted trans-1,4-cyclohexylene groups, more preferably 1 to 3, and even more preferably 2 or 3. Furthermore, as A, the polymerizable compound represented by formula (I) preferably contains one or more substituted phenylene groups, more preferably 1 to 4, even more preferably 1 to 3, and particularly preferably 2 or 3.

[0208] In formula (I), when the number obtained by dividing the quantity of trans-1,4-cyclohexyl groups represented by A by m is set as mc, it is preferably 0.1 < mc < 0.9, more preferably 0.3 < mc < 0.8, and even more preferably 0.5 < mc < 0.7. It is also preferred that the liquid crystal composition contains a polymerizable compound represented by formula (I) with a content of 0.5 < mc < 0.7, and contains a polymerizable compound represented by formula (I) with a content of 0.1 < mc < 0.3.

[0209] Examples of polymeric compounds represented by formula (I) include, in addition to the compounds described in paragraphs 0051 to 0058 of WO2016 / 047648, compounds described in Japanese Patent Application Publication No. 2013-112631, Japanese Patent Application Publication No. 2010-070543, Japanese Patent No. 4725516, WO2015 / 115390, WO2015 / 147243, WO2016 / 035873, Japanese Patent Application Publication No. 2015-163596, and Japanese Patent Application Publication No. 2016-053149.

[0210] (Chiral reagents: optically active compounds)

[0211] Chiral reagents have the function of inducing helical structures in cholesterol-type liquid crystal phases. The helix direction or helical pitch induced varies depending on the compound, thus the chiral compound can be selected according to the purpose.

[0212] There are no particular restrictions on the use of chiral reagents; known compounds can be used. Examples of chiral reagents include compounds described in various publications such as the Liquid Crystal Device Handbook (Chapter 3, Item 4-3, TN and STN using chiral reagents, page 199, compiled by Committee 142 of the Japanese Society for the Promotion of Science, 1989), Japanese Patent Application Publication No. 2003-287623, Japanese Patent Application Publication No. 2002-302487, Japanese Patent Application Publication No. 2002-080478, Japanese Patent Application Publication No. 2002-080851, Japanese Patent Application Publication No. 2010-181852, and Japanese Patent Application Publication No. 2014-034581.

[0213] Chiral reagents generally contain asymmetric carbon atoms, but axially asymmetric or surface-asymmetric compounds that do not contain asymmetric carbon atoms can also be used as chiral reagents. Examples of axially asymmetric or surface-asymmetric compounds include binaphthyl, helicene, p-cycloaranes, and their derivatives.

[0214] Chiral reagents can have polymerizable groups. When both the chiral reagent and the liquid crystal compound have polymerizable groups, a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral reagent can be formed through a polymerization reaction of the chiral reagent and the polymerizable liquid crystal compound. In this manner, the polymerizable groups possessed by the chiral reagent are preferably of the same type as those possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable groups of the chiral reagent are preferably unsaturated polymerizable groups, epoxy groups, or aziridinyl groups, more preferably unsaturated polymerizable groups, and especially preferably olefinic unsaturated polymerizable groups.

[0215] Furthermore, the chiral reagent can also be a liquid crystal compound.

[0216] As chiral reagents, isosorbide derivatives, isomannitol derivatives, and binaphthyl derivatives are preferred. For isosorbide derivatives, commercially available products such as BASF's LC756 can be used.

[0217] The content of the chiral reagent in the liquid crystal composition is preferably 0.01 to 200 mol% of the amount of the polymerizable liquid crystal compound, more preferably 1 to 30 mol%. Furthermore, the content of the chiral reagent in the liquid crystal composition indicates the concentration (mass %) of the chiral reagent relative to the total solid components in the composition.

[0218] Furthermore, as described above, the cholesteric liquid crystal layer of the selective reflection layer in the reflective film of the present invention can have two or more selective reflection center wavelengths. A cholesteric liquid crystal layer having two or more selective reflection center wavelengths is achieved by changing the pitch of the helical structure in the thickness direction. A cholesteric liquid crystal layer in which the pitch of the helical structure changes in the thickness direction can be fabricated by changing the amount of light irradiation in the thickness direction when forming a cholesteric liquid crystal layer using a chiral reagent whose helical twisting power (HTP) changes upon light irradiation.

[0219] Chiral reagents that undergo changes in HTP upon light irradiation include those that exhibit reverse isomerization, dimerization, and both isomerization and dimerization upon light irradiation.

[0220] When a chiral reagent has a photoisomerizing group, the photoisomerizing group is preferably an isomerizing site of a compound that exhibits photochromic properties, an azo group, an oxyazo group, or a cinnamoyl group. As specific compounds, compounds described in Japanese Patent Application Publication Nos. 2002-080478, 2002-080851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292 may be used.

[0221] (Polymerization initiator)

[0222] The liquid crystal composition preferably contains a polymerization initiator. In the case of polymerization reaction carried out by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator capable of initiating polymerization reaction by ultraviolet irradiation.

[0223] Examples of photopolymerization initiators include α-carbonyl compounds (described in US Patent Nos. 2,367,661 and 2,367,670), azobin ethers (described in US Patent No. 2,448,828), α-hydrocarbon-substituted aromatic azobin compounds (described in US Patent No. 2,722,512), polynuclear quinone compounds (described in US Patent Nos. 3,046,127 and 2,951,758), combinations of triarylimidazolium dimers and p-aminophenyl ketones (described in US Patent No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent Application Publication No. 60-105,667 and US Patent No. 4,239,850), and acylphosphine oxide compounds (Japanese Patent Application Publication No. 63-040,799). Japanese Patent Application Publication No. 5-029234, Japanese Patent Application Publication No. 10-095788, Japanese Patent Application Publication No. 10-029997, Japanese Patent Application Publication No. 2001-233842, Japanese Patent Application Publication No. 2000-080068, Japanese Patent Application Publication No. 2006-342166, Japanese Patent Application Publication No. 2013-114249, Japanese Patent Application Publication No. 2014- Japanese Patent Publication No. 137466, Japanese Patent Publication No. 4223071, Japanese Unexamined Patent Publication No. 2010-262028, and Japanese Unexamined Patent Publication No. 2014-500852, etc., oxime compounds (Japanese Unexamined Patent Publication No. 2000-066385 and Japanese Patent Publication No. 4454067), and oxadiazole compounds (US Patent No. 4212970). For example, see also paragraphs 0500 to 0547 of Japanese Unexamined Patent Publication No. 2012-208494.

[0224] Acylphosphine oxide compounds or oxime compounds are preferred as polymerization initiators.

[0225] As acylphosphine oxide compounds, commercially available products such as IRGACURE 810 (compound name: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) manufactured by BASF JAPAN LTD. can be used. As oxime compounds, commercially available products such as IRGACURE OXE01 (manufactured by BASF), IRGACURE OXE02 (manufactured by BASF), TR-PBG-304 (manufactured by Changzhou Qiangli Electronic New Materials Co., Ltd.), ADEKA ARKLS NCI-831, ADEKA ARKLS NCI-930 (manufactured by ADEKA CORPORATION), and ADEKA ARKLS NCI-831 (manufactured by ADEKA CORPORATION) can be used.

[0226] Polymerization initiators can be used in single or multiple ways.

[0227] The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass relative to the content of the polymerizable liquid crystal compound, more preferably 0.5 to 5% by mass.

[0228] (Cross-linking agent)

[0229] To improve the strength and durability of the cured film, the liquid crystal composition may contain a crosslinking agent. Preferably, the crosslinking agent is one that is cured by ultraviolet light, heat, or moisture.

[0230] There are no particular limitations on the crosslinking agent; it can be selected appropriately according to the purpose. Examples of crosslinking agents include: polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl methacrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-dimethylolbutanol-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 chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. Furthermore, known catalysts can be used based on the reactivity of the crosslinking agent, which can improve membrane strength and durability, as well as increase productivity. These can be used individually or in combination.

[0231] 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.

[0232] In addition, "(meth)acrylate" is used to mean "either or both of acrylate and methacrylate".

[0233] (Orientation control agent)

[0234] Orientation control agents that help stabilize or rapidly form a planar orientation of a cholesteric liquid crystal layer can 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.

[0235] In addition, as an orientation control agent, it can be used alone or two or more at the same time.

[0236] 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.

[0237] (Other additives)

[0238] Furthermore, the liquid crystal composition may 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. Additionally, polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, and metal oxide particles may be further added to the liquid crystal composition as needed, without degrading optical performance.

[0239] Cholesterol-type liquid crystal layers can be formed by coating a liquid crystal composition, which is prepared by dissolving a polymerizable liquid crystal compound and a polymerization initiator, and further adding chiral reagents and surfactants as needed, in a solvent onto a transparent substrate, a phase reversal layer, an alignment layer, or a previously prepared cholesterol-type liquid crystal layer, and then drying it to obtain a coating film. The coating film is then irradiated with activation light to polymerize the cholesterol-type liquid crystal composition, thereby forming a cholesterol-type liquid crystal layer in which the regularity of cholesterol is fixed.

[0240] In addition, a laminated film composed of multiple cholesterol-type liquid crystal layers can be formed by repeatedly performing the above-described manufacturing process of cholesterol-type liquid crystal layers.

[0241] (solvent)

[0242] There are no particular restrictions on the solvents used to prepare liquid crystal compositions, and they can be selected appropriately according to the purpose, but organic solvents are preferred.

[0243] There are no particular limitations on organic solvents; they can be selected appropriately depending on the purpose. Examples include ketones, haloalkanes, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. One or more of these can be used simultaneously. Considering the environmental impact, ketones are particularly preferred.

[0244] (Coating, Orientation, Polymerization)

[0245] There are no particular limitations on the method of coating a liquid crystal composition onto a transparent substrate, an alignment layer, or a cholesterol-type liquid crystal layer that serves as the underlayer; the method can be selected appropriately depending on the purpose. Examples of coating methods include wire-wound coating, curtain coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spin coating, dip coating, spray coating, and slide coating. Furthermore, the method can also be implemented by transferring a liquid crystal composition separately coated onto a support.

[0246] 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 polymerizable liquid crystal compound is twisted and oriented in a direction substantially perpendicular to the film surface, having a helical axis.

[0247] 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 .

[0248] To promote photopolymerization, light irradiation can be performed under heating conditions or a nitrogen atmosphere. The wavelength of the irradiated ultraviolet light is preferably 350–430 nm. From a stability point of view, a higher polymerization rate is preferred, preferably 70% or more, and more preferably 80% or more. The polymerization rate can be determined by measuring the proportion of polymerizable functional groups consumed using infrared absorption spectroscopy.

[0249] <Polarization conversion layer>

[0250] The polarization conversion layer 14 is preferably a layer formed by fixing a helical orientation structure of a liquid crystal compound, and the pitch number x of the helical orientation structure and the film thickness y (in μm) of the polarization conversion layer satisfy all the following relationships (a) to (c).

[0251] 0.1≤x≤1.0···Equation (a)

[0252] 0.5≤y≤3.0···Equation (b)

[0253] 3000≤(1560×y) / x≤50000···Equation (c)

[0254] Furthermore, one pitch of the helical structure of a liquid crystal compound is the length of one turn of the liquid crystal compound's helix. That is, 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 360° is considered to be the pitch number 1.

[0255] If the polarization conversion layer has a helical structure of a liquid crystal compound, it will exhibit optical rotation and birefringence for visible light with wavelengths shorter than the peak reflection wavelength of the infrared region. Therefore, it is possible to control the polarization of visible light. By setting the pitch number x of the helical orientation structure of the polarization conversion layer and the film thickness y of the polarization conversion layer within the above-mentioned range, it is possible to impart the function of optical compensation through the polarization conversion layer to visible light or to convert linearly polarized light (p-polarized light) incident on the reflective film into circularly polarized light.

[0256] By employing a helical structure in the liquid crystal compound that satisfies equations (a) to (c), the polarization conversion layer exhibits optical rotation and birefringence with respect to visible light. In particular, by setting the pitch P of the helical structure of the polarization conversion layer to a length corresponding to the pitch P of a cholesteric liquid crystal layer in the long-wavelength infrared region, it exhibits high optical rotation and high birefringence with respect to short-wavelength visible light.

[0257] The relation (a) is “0.1≤x≤1.0”.

[0258] If the pitch number x of the helical structure is less than 0.1, undesirable conditions such as insufficient optical rotation and birefringence may occur.

[0259] Furthermore, if the pitch number x of the spiral structure exceeds 1.0, adverse situations may occur, such as the inability to obtain the desired elliptically polarized light due to excessive optical rotation and birefringence.

[0260] The relation (b) is “0.5≤y≤3.0”.

[0261] If the thickness y of the polarization conversion layer is less than 0.5 μm, problems such as insufficient optical rotation and birefringence will occur due to the film being too thin.

[0262] If the thickness y of the polarization conversion layer exceeds 3.0 μm, adverse situations may occur, such as the inability to obtain the desired circularly polarized light due to excessive optical rotation and birefringence, and poor orientation, which is not preferred from a manufacturing perspective.

[0263] The relation (c) is “3000≤(1560×y) / x≤50000”.

[0264] If "(1560×y) / x" is less than 3000, adverse situations such as failure to obtain the desired polarized light due to excessive optical rotation may occur.

[0265] If "(1560×y) / x" exceeds 50000, undesirable situations may occur, such as the inability to obtain the desired polarized light due to insufficient optical rotation.

[0266] In this invention, the pitch number x of the spiral structure of the polarization conversion layer is more preferably 0.1 to 0.8, and the film thickness y is more preferably 0.6 μm to 2.6 μm. Furthermore, "(1560×y) / x" is more preferably 5000 to 13000.

[0267] That is, the preferred polarization conversion layer has a long pitch P and a small number of pitches x in a spiral structure.

[0268] Specifically, the pitch P of the preferred helix of the polarization conversion layer is equal to the pitch P of the cholesteric liquid crystal layer whose selective reflection center wavelength is in the long-wavelength infrared region, and the number of pitches x is small. More specifically, the pitch P of the preferred helix of the polarization conversion layer is equal to the pitch P of the cholesteric liquid crystal layer whose selective reflection center wavelength is 3000-10000 nm, and the number of pitches x is small.

[0269] The selective reflection center wavelength corresponding to the pitch P of this polarization conversion layer is much longer than that of visible light, thus it can more appropriately exhibit optical rotation and birefringence for the aforementioned visible light.

[0270] This polarization conversion layer can be formed in essentially the same way as the known cholesterol-type liquid crystal layer. However, in forming the polarization conversion layer, in order to make the pitch number x and film thickness y [μm] of the helical structure in the polarization conversion layer satisfy all the relationships in equations (a) to (c), it is necessary to adjust the liquid crystal compound used, the chiral reagent used, the amount of chiral reagent added, and the film thickness.

[0271] <Layer formed by fixing the helical orientation structure (helical structure) of liquid crystal compound>

[0272] A layer formed by fixing the helical orientation structure (helical structure) of a liquid crystal compound is called a cholesterol-type liquid crystal layer, which means a layer formed by fixing a cholesterol-type liquid crystal phase.

[0273] A cholesterol-type liquid crystal layer is simply a layer that can maintain the orientation of the liquid crystal compound, which 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 into a cholesterol-type liquid crystal phase after it has been oriented to that state, through ultraviolet irradiation and heating, to render it non-flowable and simultaneously change its orientation morphology to a state that will not change due to external fields or forces. Furthermore, in a cholesterol-type liquid crystal layer, it is sufficient that the optical properties of the cholesterol-type liquid crystal phase are maintained within the layer; the liquid crystal compound within the layer may no longer exhibit liquid crystal properties. For example, the polymerizable liquid crystal compound can be molecularized through a curing reaction, thereby losing its liquid crystal properties.

[0274] As described above, the selective reflection center wavelength λ of a cholesterol-type liquid crystal layer depends on the pitch P (=helical period) 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. According to this formula, the selective reflection center wavelength can be adjusted by adjusting the value of n and / or the value of P.

[0275] The helical pitch of a cholesterol-type liquid crystal phase depends on the type and concentration of the chiral reagent used with the polymerizable liquid crystal compound, and therefore the desired pitch can be obtained by adjusting these.

[0276] As described above, the cholesterol-type liquid crystal layer used as a polarization conversion layer adjusts the helical pitch to select the reflection center wavelength in the long-wavelength infrared region.

[0277] The method for forming the cholesterol-type liquid crystal layer, which serves as the polarization conversion layer, is basically the same as the method for forming the cholesterol-type liquid crystal layer described above.

[0278] <Phase Difference Layer>

[0279] The phase difference layer adds a phase difference (optical path difference) to two orthogonal polarized light components to change the state of the incident polarized light.

[0280] When the phase difference layer is configured on the outside of the vehicle to perform optical compensation, the front phase difference of the phase difference layer only needs to be a phase difference that can be optically compensated.

[0281] In this case, the phase retardation layer preferably has a frontal delay of 50 nm to 160 nm at a wavelength of 550 nm.

[0282] Furthermore, when the windshield with the reflective film is installed on the vehicle, and the direction above the vertical direction corresponding to the surface of the first glass panel is set to 0°, the angle of the slow axis is preferably 10° to 50° or -50° to -10°.

[0283] Furthermore, when the phase retardation layer is a phase retardation layer that converts linearly polarized light into circularly polarized light, the phase retardation layer is preferably composed of an object with a frontal phase retardation of λ / 4, but it can also be composed of an object providing a frontal phase retardation of 3λ / 4. Moreover, the angle of the slow axis only needs to be configured to change the direction of the incident linearly polarized light into circularly polarized light.

[0284] In this case, the phase retardation layer preferably has a frontal phase retardation in the range of 100 to 450 nm at a wavelength of 550 nm, more preferably in the range of 120 to 200 nm or 300 to 400 nm. Furthermore, the direction of the slow axis of the phase retardation layer is preferably determined based on the incident direction of the projection light used to display the projected image when the reflective film 10 is used in a head-up display system and the direction of the spiral of the cholesteric liquid crystal layer constituting the selective reflective layer.

[0285] There are no particular limitations on the retardation layer, and 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 for orientation, thin films formed by tilting the deposition of inorganic dielectrics on a support, films that fix the orientation of polymeric liquid crystal compounds by uniaxial orientation, and films that fix the orientation of liquid crystal compounds by uniaxial orientation.

[0286] Among them, the film in which the polymeric liquid crystal compound is uniaxially oriented and its orientation is fixed is preferably exemplified as a phase retardation layer.

[0287] As an example, 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 transparent substrate, a pseudo-support, or an alignment layer; then, after the polymeric liquid crystal compound in the liquid crystal composition is oriented in a nematic state in a liquid crystal state, it is fixed by curing.

[0288] Except for the absence of a chiral reagent in the liquid crystal composition, the formation of the retardation layer in this case can be carried out in the same manner as the formation of the cholesterol-type liquid crystal layer described above. Specifically, during nematic alignment after coating the liquid crystal composition, the heating temperature is preferably 50–120°C, more preferably 60–100°C.

[0289] The phase retardation layer can be formed by coating a composition containing a polymer liquid crystal compound onto the surface of a transparent substrate, a pseudo-support, or an alignment layer, forming a nematic alignment in a liquid crystal state, and then cooling to fix the alignment.

[0290] The thickness of the retardation layer is not limited, but is preferably 0.2 to 300 μm, more preferably 0.5 to 150 μm, and even more preferably 1.0 to 80 μm. The thickness of the retardation layer formed from the liquid crystal composition is not particularly limited, but is preferably 0.2 to 10 μm, more preferably 0.5 to 5.0 μm, and even more preferably 0.7 to 2.0 μm.

[0291] The slow axis of the retardation layer is set, for example, by tilting it at an angle α relative to an axis in any direction of the retardation layer. The direction of the slow axis can be set, for example, by friction treatment of the alignment film that becomes the bottom layer of the retardation layer.

[0292] The reflective film of the present invention may have layers other than a selective reflective layer, a polarization conversion layer, and a phase difference layer. For example, the reflective film may have a transparent substrate, an adhesive layer, etc.

[0293] For example, in Figure 1 In the example shown, the reflective film 10 has a transparent substrate 18 disposed on the side of the retardation layer 16 opposite to the selective reflective layer 11. The transparent substrate 18 supports the retardation layer 16, the selective reflective layer 11 (cholesterol-type liquid crystal layer), and the polarization conversion layer 14. The transparent substrate 18 can be used as a support when forming the retardation layer 16, the selective reflective layer 11 (cholesterol-type liquid crystal layer), and the polarization conversion layer 14.

[0294] Reflective films can be in the form of thin films or sheets. They can also be rolled up in thin film form before being applied to windshields.

[0295] The transparent substrate and adhesive layer are preferably transparent in the visible light region.

[0296] Furthermore, the transparent substrate and adhesive layer are preferably low birefringence. Low birefringence means that the frontal phase difference in the wavelength region where the reflective film of the windshield of the present invention exhibits reflection is less than 10 nm. This frontal phase difference is preferably less than 5 nm. Moreover, the difference between the refractive index of the support and adhesive layer and the average refractive index (in-plane average refractive index) of the selected reflective layer is preferably small.

[0297] <Transparent substrate>

[0298] A transparent substrate can also be used as a substrate when forming a selective reflective layer. The transparent substrate used to form the selective reflective layer can be a dummy support that is peeled off after the selective reflective layer is formed. Therefore, the finished reflective film and windshield may not include a transparent substrate. Furthermore, when the finished reflective film or windshield includes a transparent substrate instead of being peeled off as a dummy support, the transparent substrate is preferably transparent in the visible light region.

[0299] There are no restrictions on the materials used for the transparent substrate. Examples of transparent substrates include polyesters such as polyethylene terephthalate (PET), polycarbonate, acrylic resins, epoxy resins, polyurethanes, polyamides, polyolefins, cellulose derivatives, and silicone films. In addition to the aforementioned plastic films, glass can also be used as a pseudo-support.

[0300] The thickness of the transparent substrate can be about 5.0 to 1000 μm, preferably 10 to 250 μm, and more preferably 15 to 90 μm.

[0301] Here, as Figure 3As shown in the example, when the transparent substrate 18 is disposed on the side of the second glass plate 30 (i.e., the outside of the vehicle), the transparent substrate 18 preferably contains an ultraviolet absorber.

[0302] By including a UV absorber in the transparent substrate 18, the degradation of the reflective film (selective reflective layer) due to UV radiation can be suppressed.

[0303] Laminated Glass

[0304] The windshield may have a laminated glass structure. The windshield of the present invention is preferably laminated glass, and the reflective film of the present invention described above is provided between the first glass plate and the second glass plate.

[0305] The windshield may have 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 at at least at one of the locations between the first glass panel and the reflective film and between the reflective film and the second glass panel.

[0306] In the windshield, as an example, the second glass panel is positioned on the side of the HUD opposite to the visual recognition side of the image (outer side of the vehicle), while the first glass panel is positioned 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 are not technically significant but are provided for ease of distinguishing the two glass panels. Therefore, it is also possible for the second glass panel to be on the inner side of the vehicle and the first glass panel to be on the outer side of the vehicle.

[0307] The first and second glass plates, etc., can be glass plates commonly used for windshields. For example, glass plates with visible light transmittance of 73% and 76% or less, or even 80% or less, such as high-heat-insulating green glass, can 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.

[0308] There are no particular limitations 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 materials or thicknesses of the first and second glass plates can be the same or different.

[0309] Windshields with laminated glass structures can be manufactured using known methods for making laminated glass.

[0310] Typically, it can be manufactured by sandwiching laminated glass between two glass plates with an interlayer film, repeatedly subjecting it to heat treatment and pressure treatment (such as treatment using rubber rollers), and finally using an autoclave or similar device for heat treatment under pressure.

[0311] 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 a 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.

[0312] 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 can be adhered to the glass plate, for example, using an adhesive (heat-sealing layer).

[0313] (Intermediate membrane)

[0314] Interlayer 36 is used to prevent glass from entering the vehicle and splattering in the event of an accident. Figure 3 In the example shown, it is used to bond the reflective film 10 and the first glass plate 28.

[0315] As the interlayer (interlayer film), any known interlayer used as an interlayer (interlayer) in laminated glass can be used. For example, a resin film containing a resin selected from the group consisting of polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, and 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.

[0316] 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.

[0317] Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol using butyral. The preferred lower limit for 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%.

[0318] Polyvinyl alcohol is usually obtained by saponifying polyvinyl acetate, typically using polyvinyl alcohol with a saponification degree of 80 to 99.8 mol%.

[0319] 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 resulting laminated glass is not easily reduced; if it is below 3000, the resin film has good formability, and the rigidity of the resin film does not become too large, thus resulting in good processability. A more preferred lower limit is 500, and a more preferred upper limit is 2000.

[0320] Furthermore, the thickness of the interlayer 36 is not limited; it can be set to the same thickness as the interlayer of a known windshield, corresponding to the forming material, etc.

[0321] In addition, the windshield 24 has a heat-sealing layer 38 between the reflective film 10 and the second glass plate 30, and the reflective film 10 and the first glass plate 28 are attached with an interlayer film 36, but it is not limited to this. That is, it can also have the following structure: a heat-sealing layer is provided between the reflective film 10 and the first glass plate 28, and an interlayer film is provided between the reflective film 10 and the second glass plate 30.

[0322] Alternatively, the windshield 24 may have the following structure: the windshield 24 does not have an interlayer 36, and the reflective film 10 and the first glass plate 28 and the reflective film 10 and the second glass plate 30 are attached using a heat-sealing layer 38.

[0323] (Including the intermediate film of the reflective film)

[0324] Interlayers for laminated glass, including reflective films, can be formed by laminating the reflective film onto the surface of the aforementioned interlayers. Alternatively, they can be formed by sandwiching the reflective film between two aforementioned interlayers. The two interlayers can be identical or different, but are preferably identical.

[0325] When laminating the reflective film and the interlayer, known lamination methods can be used, but a lamination process is preferred. The lamination process is preferably carried out under certain heating and pressure conditions to prevent the laminate and the interlayer from peeling off after processing.

[0326] To ensure stable lamination, the surface temperature of the interlayer on the bonding side is preferably 50–130°C, more preferably 70–100°C.

[0327] During lamination, pressure is preferably applied. There are no restrictions on the pressure conditions, but it is preferred to be less than 2.0 kg / cm³. 2 (less than 196 kPa), more preferably 0.5–1.8 kg / cm². 2 (49–176 kPa), more preferably 0.5–1.5 kg / cm². 2 (49~147kPa).

[0328] Furthermore, when the reflective film has a support (transparent substrate), the support can be peeled off during lamination, immediately after lamination, or just before lamination. That is, the reflective film attached to the intermediate film obtained after lamination may not have a support.

[0329] An example of a method for manufacturing an intermediate film including a reflective film includes:

[0330] (1) In the first step, a reflective film is laminated onto the surface of the first intermediate film to obtain the first laminate; and

[0331] (2) The second step is to attach the second intermediate film to the side opposite to the side of the reflective film in the first laminate that is attached to the first intermediate film.

[0332] For example, in the first step, the reflective film and the first intermediate film are bonded together without the support and the first intermediate film facing each other. Next, the support is peeled off from the reflective film. Then, in the second step, the second intermediate film is bonded to the surface after the support has been peeled off. Thus, an intermediate film including a reflective film without a support can be manufactured. Furthermore, using this intermediate film including the reflective film, laminated glass with a reflective film that does not have a support can be easily manufactured.

[0333] In order to stably peel off the support without damaging it, the temperature of the support when peeling it off from the reflective film is preferably 40°C or higher, and more preferably 40 to 60°C.

[0334] (Heat-sealing layer)

[0335] The heat-sealing layer (adhesive layer) 38 is, for example, a layer composed of a coating adhesive. Figure 3 In the example shown, the reflective film 10 is attached to the second glass plate 30 via a heat-sealing layer 38. Alternatively, in the windshield of the present invention, the reflective film 10 can be attached to the second glass plate 30 via an interlayer film instead of the heat-sealing layer 38. Furthermore, if the reflective film 10 is smaller than the interlayer film 36 on which the first glass plate 28 and the reflective film 10 are attached, the reflective film 10 can also be attached to the second glass plate 30 via the interlayer film 36.

[0336] There are no limitations on the heat-sealing layer 38. As long as the required transparency of the windshield 24 can be ensured, and the reflective film 10 and the glass can be adhered with the necessary adhesion, various known adhesive layers composed of coating-type adhesives can be used. The heat-sealing layer 38 can use materials such as PVB, which are the same as the interlayer film 36. In addition, the heat-sealing layer 38 can also use acrylic adhesives, etc.

[0337] The heat-sealing layer 38 can be formed by an adhesive.

[0338] 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, any type of adhesive can use compounds such as acrylates, urethanes, urethane acrylates, epoxy compounds, epoxy acrylates, polyolefins, modified olefins, polypropylenes, ethylene-vinyl alcohol, vinyl chloride, chloroprene rubber, cyanoacrylates, polyamides, polyimides, polystyrene, and polyvinyl butyral as raw materials.

[0339] From the perspective of operability and productivity, light-curing is preferred as the curing method. From the perspective of optical transparency and heat resistance, acrylate-based, urethane acrylate-based, and epoxy acrylate-based raw materials are preferred.

[0340] The heat-sealing layer 38 can be a layer formed using a high-transparency adhesive transfer tape (OCA tape). As a high-transparency adhesive transfer tape, commercially available products for image display devices can be used, especially those for the surface of the image display section of an image display device. Examples of commercially available products include adhesive sheets (PD-S1, etc.) manufactured by PANAC Co., Ltd., and MHM series adhesive sheets from NICHIEI KAKOH CO.,LTD.

[0341] There is no limitation on the thickness of the heat-sealing layer 38. Therefore, by appropriately setting the thickness according to the forming material of the heat-sealing layer 38, sufficient adhesion can be obtained.

[0342] If the heat-sealing layer 38 is too thick, it may be impossible to attach the reflective film 10 to the first glass plate 28 or the second glass plate 30 while ensuring sufficient planarity. With this in mind, the thickness of the heat-sealing layer 38 is preferably 0.1 to 800 μm, more preferably 0.5 to 400 μm.

[0343] Next, a head-up display (HUD) having the reflective film of the present invention will be described.

[0344] The head-up display of the present invention is a head-up display system having:

[0345] The aforementioned windshield; and

[0346] The projector shines a projected image onto the first glass panel of the windshield.

[0347] Figure 5 An example of the head-up display of the present invention is shown in the figure.

[0348] Figure 5 The HUD20 shown has a windshield 24 and a projector 22. The HUD20 is used, for example, in vehicles such as cars.

[0349] Windshield 24 has with Figure 3 The windshield 24 shown has the same structure.

[0350] In a HUD 20 using the reflective film 10 of the present invention, a projector 22 emits p-polarized projection light, and the reflective film 10 reflects the p-polarized light, thereby displaying an image.

[0351] Specifically, in the reflective film 10, firstly, the polarization conversion layer 14 converts the incident p-polarized projection light into circularly polarized light. Next, the selective reflective layer 11 (cholesterol-type liquid crystal layer) selectively reflects this circularly polarized light, causing it to re-enter the polarization conversion layer 14. Then, the polarization conversion layer 14 converts the circularly polarized light back into p-polarized light. Thus, the reflective film 10 reflects the incident p-polarized projection light in its original p-polarized form.

[0352] Therefore, the polarization conversion layer 14 is configured to convert incident p-polarized light into circularly polarized light with the rotation direction reflected by the selective reflection layer 11 (cholesterol-type liquid crystal layer) based on the rotation direction of the circularly polarized light selectively reflected by the selective reflection layer 11. That is, when the selective reflection layer 11 selectively reflects right-hand circularly polarized light, the phase retardation layer is configured to make the incident p-polarized light become right-hand circularly polarized light. Conversely, when the selective reflection layer 11 selectively reflects left-hand circularly polarized light, the phase retardation layer is configured to make the incident p-polarized light become left-hand circularly polarized light.

[0353] In HUD 20, projector 22 preferably projects p-polarized projection light onto windshield 24 (second glass plate 30). By setting the projection light projected by projector 22 onto windshield 24 to p-polarized light, the amount of projection light reflected by the second glass plate 30 and the first glass plate 28 of windshield 24 can be significantly reduced, thereby suppressing the observation of ghosting and other undesirable conditions.

[0354] Preferably, the projector 22 projects p-polarized projection light onto the windshield at a Brewster angle. This eliminates reflections of the projection light on the second glass plate 30 and the first glass plate 28, thereby enabling the display of a clearer image.

[0355] Projector

[0356] "Projector" is a "device for projecting light or an image," including "devices for projecting a depicted image," and emits projection light carrying the image to be displayed. In the HUD of the present invention, the projector preferably emits p-polarized projection light.

[0357] In a HUD, the projector only needs to be configured to allow the p-polarized projection light carrying the image to be displayed to be incident at an angle onto the reflective film in the windshield.

[0358] In a HUD, the projector preferably includes a drawing device and a combiner reflects the image (real image) drawn on a small intermediate image screen as a virtual image.

[0359] As long as the projector can emit p-polarized projection light, any known projector used for HUDs can be used. Furthermore, the projector preferably has a variable imaging distance for the virtual image (i.e., the imaging position of the virtual image).

[0360] Methods for changing the imaging distance of the virtual image in a projector include, for example, moving the image generating 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 reflector, changing the focal length by using a lens group as an imaging lens, moving the projector 22, switching between multiple projectors with different imaging distances of the virtual image, and using a zoom lens (see WO2010 / 116912), etc.

[0361] In addition, the projector can be a projector that can continuously change the imaging distance of the virtual image, or a projector that can switch the imaging distance of the virtual image between multiple points, such as two or three points.

[0362] Here, in the virtual image of the projected light projected by the projector, it is preferable that the imaging distances of at least two virtual images differ by more than 1 meter. Therefore, when the projector is capable of continuously changing 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 driver's line of sight distance differs greatly, such as when driving at normal speeds on ordinary roads and driving at high speeds on highways.

[0363] (Description of the device)

[0364] A drawing device can be a device that displays an image for itself, or it can be a device that emits light capable of drawing an image.

[0365] In a drawing device, light from a light source can be adjusted using drawing methods such as an optical modulator, a laser brightness modulation mechanism, or a light deflection mechanism for drawing. A drawing device refers to a device that includes a light source and, depending on the drawing method, also includes an optical modulator, a laser brightness modulation mechanism, or a light deflection mechanism for drawing.

[0366] (light source)

[0367] There are no restrictions on the light source; known light sources used in projectors, drawing devices, and displays, such as LEDs (light-emitting diodes), organic light-emitting diodes (OLEDs), discharge tubes, and laser light sources, can be used.

[0368] LEDs and discharge tubes are suitable as light sources for drawing devices that emit linearly polarized light, and therefore LEDs are preferred, and especially preferred. This is because the emission wavelength of LEDs is not continuous in the visible light region, and therefore they are suitable for combination with a combiner that uses a cholesterol-type liquid crystal layer that exhibits selective reflection in a specific wavelength region, as described later.

[0369] (Description method)

[0370] The method of depiction can be chosen based on the light source used, and there are no particular limitations.

[0371] Examples of display methods include fluorescent tubes, LCD (Liquid Crystal Display) and LCOS (Liquid Crystal on Silicon) displays using liquid crystals, DLP (Digital Light Processing) displays, and laser scanning methods. A fluorescent tube display, where the light source is integrated with the display, can be used. LCD displays are preferred as a display method.

[0372] In LCD and LCOS modes, light of different colors is modulated and combined by a light modulator and then emitted from the projection lens.

[0373] The DLP method uses a display system with a DMD (Digital Micromirror Device), which is equipped with micromirrors equivalent to the number of pixels to depict images and emits light from a projection lens.

[0374] The scanning method involves scanning light on a screen and creating an image using the afterimages seen by the naked eye. For example, see Japanese Patent Application Publication Nos. 7-270711 and 2013-228674. In laser-based scanning, laser beams of various colors (e.g., red, green, and blue light) modulated by brightness can be focused into a single beam using a beam-combining optical system or a focusing lens. This beam is then scanned by a light deflection mechanism and projected onto an intermediate image screen, as described later.

[0375] In the scanning method, the brightness modulation of the laser beams of each color (e.g., red, green, and blue light) can be performed directly as a change in the intensity of the light source, or it can be performed through an external modulator. Examples of light deflection mechanisms include galvanometer mirrors, combinations of galvanometer mirrors and prisms, and MEMS (Micro Electro Mechanical Systems), with MEMS being preferred. Examples of scanning methods include random scanning and grating scanning, with grating scanning being preferred. In grating scanning, for example, the laser beam can be driven at a resonant frequency in the horizontal direction and driven with a sawtooth wave in the vertical direction. The scanning method does not require a projection lens, thus facilitating device miniaturization.

[0376] The emitted light from the drawing device can be linearly polarized light or natural light (unpolarized light).

[0377] 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 from the drawing device is linearly polarized and includes multiple wavelengths (colors), the polarization directions (transmission axis directions) of the multiple wavelengths are preferably the same. It is known that the polarization directions of commercially available drawing devices are sometimes not uniform in the wavelength regions of red, green, and blue light emitted as the emitted light (see Japanese Patent Application Laid-Open No. 2000-221449). Specifically, there is a known example where the polarization direction of green light is orthogonal to the polarization directions of red and blue light.

[0378] Furthermore, in the HUD of the present invention, the projection light emitted by the projector is preferably p-polarized light for the reasons stated above.

[0379] (The middle part resembles a screen)

[0380] As described above, the drawing device can be a device that uses an intermediate image screen. An "intermediate image screen" is a screen on which an image is drawn. That is, even when the light emitted from the drawing device is not yet visually recognizable as an image, the drawing device uses this light to form a visually recognizable image on the intermediate image screen. The image drawn on the intermediate image screen can be projected onto the combiner by light transmitted through the intermediate image screen, or it can be reflected from the intermediate image screen and projected onto the combiner.

[0381] Examples of intermediate image screens include scattering films, microlens arrays, and rear projection screens. When plastic materials are used as intermediate image screens, if the intermediate image screen is birefringent, the polarization plane and intensity of the polarized light incident on the intermediate image screen will be disturbed, which can easily cause 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.

[0382] As an intermediate image screen, an intermediate image screen that diffuses incident light for its transmission is preferred. This is because it allows for the magnification of the projected image. Examples of such an intermediate image screen include screens composed of microlens arrays. Microlens arrays used in HUDs are described, for example, in Japanese Patent Application Publication Nos. 2012-226303, 2010-145745, and 2007-523369.

[0383] Projectors may also include reflectors that adjust the optical path of the projected light formed by the drawing device.

[0384] For HUDs that use windshields as reflective films, please refer to 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.

[0385] 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) with discontinuous emission wavelengths in the visible light region. This is because the selective reflection center wavelength of the cholesteric liquid crystal layer can be adjusted according to each emission wavelength. Furthermore, it can also be used for projection onto displays that show light polarization, such as LCDs (liquid crystal displays).

[0386] [Projected light (incident light)]

[0387] 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 the glass with a refractive index of about 1.51 and the air with a refractive index of 1 is about 56°. By incident p-polarized light within the above angle range, it is possible to display an image in which there is less reflected light from the surface of the windshield relative to the selective reflective layer on the visual recognition side, thereby minimizing the effect of ghosting.

[0388] The aforementioned angle is preferably 50° to 65°. In this case, the structure can be such that the projected image can be observed at an angle of 45° to 70° (preferably 50° to 65°) on the side of the incident light relative to the normal of the selective reflective layer and opposite to the incident light.

[0389] Incident light can enter from any direction on the windshield, such as up, down, left, or right, as long as it corresponds to the direction of visual perception. For example, a preferred structure is one in which the light enters from below at the angle of incidence described above.

[0390] Furthermore, the reflective film of the windshield is preferably configured to reflect incident p-polarized light.

[0391] As described above, the projection light used to display the projected image in the HUD of the present invention is preferably p-polarized light that vibrates in a direction parallel to the incident plane.

[0392] When the projector's emitted light is not linearly polarized, it can be made p-polarized by placing a linear polarizing film (polarizer) on the projector's emitted light side, or by using known methods such as a linear polarizing film in the optical path from the projector to the windshield. In this case, the component that makes the non-linearly polarized projected light p-polarized is also considered as a component constituting the projector in the HUD of the present invention.

[0393] As described above, for a projector in which the polarization direction of the emitted light is non-uniform in the wavelength regions of red, green, and blue light, it is preferable to selectively adjust the polarization direction of the light so that it is incident as p-polarized light in the wavelength regions of all colors.

[0394] As mentioned above, a HUD (head-up display) can be a projection system where the position of the virtual image is variable. By making the position of the virtual image variable, the driver can visually identify the virtual image more comfortably and conveniently.

[0395] The virtual image imaging position is the position where the driver of the vehicle can visually identify the virtual image. It is usually viewed from the driver's side, for example, at a position more than 1000mm in front of the windshield.

[0396] 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 a direction in which the ground side is defined as the lower side and the opposite side as the upper side. Additionally, when the windshield 24 is mounted on a vehicle, it may sometimes be mounted at an angle for structural or design reasons. In this case, the vertical direction Y is the direction along the surface of the windshield 24. The surface refers to the outer surface of the vehicle.

[0397] The present invention is basically constructed as described above. The reflective film, windshield, and head-up display (HUD) of the present invention have been described in detail above, but the present invention is not limited to the above embodiments, and various improvements or modifications can be made without departing from the spirit of the present invention.

[0398] Example

[0399] The following examples further illustrate the features of the present invention. The materials, reagents, quantities, proportions, and operations shown in the following examples can 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.

[0400] <Preparation of Coating Solution>

[0401] (Coating solution for forming cholesterol-type liquid crystal layers)

[0402] Regarding multiple coating solutions for forming cholesterol-type liquid crystal layers (B1, B2, G1-G5, R1-R6, IR1-IR3) with the desired wavelength of the selective reflection center as shown in Table 1 below, coating solutions for forming cholesterol-type liquid crystal layers with the following compositions are prepared by mixing the following components.

[0403] Mixture 1 100 parts by weight

[0404] Fluorine-based horizontal orientation agent 1 (orientation control agent 1) 0.05 parts by weight

[0405] Fluorine-based horizontal orientation agent 2 (orientation control agent 2) 0.02 parts by weight

[0406] • Dextrorotatory chiral reagent LC756 (manufactured by BASF)

[0407] Adjusted according to the target reflection wavelength; polymerization initiator IRGACURE OXE01 (manufactured by BASF).

[0408] 1.0 parts by weight of solvent (methyl ethyl ketone) to a solute concentration of 20% by weight [Chemical Formula 3]

[0409] Mixture 1

[0410]

[0411] [Chemical Formula 4]

[0412] Orientation control agent 1

[0413]

[0414] [Chemical Formula 5]

[0415] Orientation control agent 2

[0416]

[0417] By adjusting the formulation amount of the dextrorotatory chiral reagent LC756 in the above coating solution, coating solutions for forming various cholesterol-type liquid crystal layers were prepared.

[0418] Using the coating solutions for forming each cholesterol-type liquid crystal layer, monolayers of each cholesterol-type liquid crystal layer with a film thickness of 3 μm were fabricated on the dummy support in the same manner as when fabricating a semi-reflective mirror as shown below, and the light reflection characteristics in the visible region were confirmed.

[0419] As a result, it was confirmed that all the cholesterol-type liquid crystal layers produced were right-circularly polarized light reflective layers, and the center wavelength of the reflection was selected as shown in Table 1 below.

[0420] (Coating solution 2 for forming cholesterol-type liquid crystal layer)

[0421] Regarding the coating solutions for forming various cholesterol-type liquid crystal layers (B3, G6, R7, IR4) with the desired wavelength of the selective reflection center as shown in Table 1 below, narrow-band cholesterol-type liquid crystal layer forming coating solutions with the following compositions are prepared by mixing the following components.

[0422]

[0423]

[0424] Rod-shaped liquid crystal compound 101

[0425] [Chemical Formula 6]

[0426]

[0427] Rod-shaped liquid crystal compound 102

[0428] [Chemical Formula 7]

[0429]

[0430] Rod-shaped liquid crystal compound 201 Rod-shaped liquid crystal compound 202

[0431] [Chemical Formula 8]

[0432] Rod-shaped liquid crystal compound 201

[0433]

[0434] Rod-shaped liquid crystal compound 202

[0435]

[0436] Orientation control agent 3

[0437] [Chemical Formula 9]

[0438]

[0439] By adjusting the formulation amount of the dextrorotatory chiral reagent LC756 in the above-mentioned narrowband cholesterol liquid crystal layer forming composition, coating solutions for forming various cholesterol liquid crystal layers were prepared.

[0440] Using the coating solutions for forming each cholesterol-type liquid crystal layer, monolayers of each cholesterol-type liquid crystal layer with a film thickness of 3 μm were fabricated on the dummy support in the same manner as when fabricating a semi-reflective mirror as shown below, and the light reflection characteristics in the visible region were confirmed.

[0441] As a result, it was confirmed that all the cholesterol-type liquid crystal layers produced were right-circularly polarized light reflective layers, and the center wavelength of the reflection was selected as shown in Table 1 below.

[0442] [Table 1]

[0443]

[0444] (Coating solution C1 for forming cholesterol-type liquid crystal layers)

[0445] Regarding the coating solution C1 for forming a cholesterol-type liquid crystal layer C1 having multiple selective reflection center wavelengths, the coating solution C1 for forming a cholesterol-type liquid crystal layer with the following composition is prepared by mixing the following components.

[0446]

[0447] Dextrorotatory isomerization chiral reagent 1

[0448] [Chemical Formula 10]

[0449]

[0450] Polymerization initiator PM7957

[0451] [Chemical Formula 11]

[0452]

[0453] (Coating solution for forming phase difference layer)

[0454] A coating solution for forming a phase difference layer with the following composition is prepared by mixing the following components.

[0455]

[0456]

[0457] A coating solution for forming a polarization conversion layer with the following composition is prepared by mixing the following components.

[0458]

[0459] After forming a cholesterol-type liquid crystal layer by adjusting the formulation amount of the dextrorotatory chiral reagent LC756 in the above-mentioned coating solution, the polarization conversion layer forming coating solution was prepared to achieve the desired selective reflection center wavelength λ. The selective reflection center wavelength λ was determined by fabricating a 3 μm thick monolayer of cholesterol-type liquid crystal layer on a pseudo-support and measuring it using FTIR (manufactured by PerkinElmer Co., Ltd., Spectrum Two).

[0460] The film thickness *d* of the 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 of the helical structure, which is one pitch when the liquid crystal compound is rotated 360° through a helical orientation. Furthermore, in a cholesterol-type liquid crystal layer, 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* is "the selective reflection center wavelength *λ* / the average in-plane refractive index *n*" (P = λ / n).

[0461] Therefore, after forming a cholesterol-type liquid crystal layer, the coating solution for forming the polarization conversion layer is prepared to select the reflection center wavelength λ as the desired wavelength. When forming the polarization conversion layer described later, the coating solution for forming the polarization conversion layer is applied to a desired film thickness to form the polarization conversion layer, and the pitch number is determined.

[0462] Table 2 shows the combination of pitch number, film thickness, and selected reflection center wavelength λ (center wavelength λ) of the polarization conversion layer formed using the coating liquid as the target.

[0463] [Table 2]

[0464]

[0465] [Example 1]

[0466] <Saponification of cellulose acylated membranes>

[0467] A cellulose acylated membrane with a thickness of 40 μm was prepared using the same method as in Example 20 of International Publication No. 2014 / 112575. Additionally, UV-531 manufactured by Yancheng Disheng Chemical Co., Ltd. was added to the cellulose acylated membrane as a UV absorber. The addition amount was set at 3 phr (per hundred parts resin).

[0468] The prepared cellulose acylated membrane is passed through a dielectric heating roller at 60°C to raise the membrane surface temperature to 40°C. Then, a bar coater is used to coat one side of the membrane at a rate of 14 mL / m. 2 The following alkaline solution with the specified coating amount was applied and placed in a steam-type far-infrared heater (manufactured by Noritake Co., Ltd.) heated to 110°C for 10 seconds.

[0469] Next, a rod coater was used to coat 3 mL / m of pure water. 2 .

[0470] Next, after repeated washing with water using a spray coating machine and dehydration using an air knife three times, the mixture is dried in a drying zone at 70°C for 5 seconds to produce a saponified cellulose acylated membrane.

[0471] The in-plane phase difference of the saponified cellulose acylated membrane measured by AxoScan was 1 nm.

[0472]

[0473]

[0474] <Formation of Orientation Film>

[0475] A coating solution for orientation film formation with the following composition (24 mL / m) was applied to the saponified surface of a saponified cellulose acylate membrane (transparent support) using a wire-wound bar coating machine. 2 It was then dried with warm air at 100°C for 120 seconds.

[0476]

[0477] (Modified polyvinyl alcohol)

[0478] [Chemical Formula 12]

[0479]

[0480] <Fabrication of Reflective Film>

[0481] A cellulose acylated membrane with an oriented film is used as a support (transparent substrate).

[0482] Friction treatment was applied to one side of the support body along a 45° clockwise rotation with the long side of the support body as the reference (artificial fiber cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm (revolutions per minute), transmission speed: 10 m / min, number of times: 1 reciprocation).

[0483] After applying a phase retardation layer coating solution to the rubbed surface of the orientation film on the support using a wire rod, the coating was dried.

[0484] Next, it was placed on a hot plate at 50°C, and in an environment with an oxygen concentration below 1000ppm, an electrodeless lamp, a "D bulb" (60mW / cm²), manufactured by Fusion UV Systems, INC., was used. 2 The liquid crystal phase was fixed by irradiating it with ultraviolet light for 6 seconds. This resulted in a phase retardation layer with its thickness adjusted to achieve the desired frontal phase retardation (i.e., the desired delay).

[0485] The delay of the fabricated phase retardation layer, measured using AxoScan, was 126 nm (Example 1).

[0486] At room temperature, a cholesterol-type liquid crystal layer forming coating solution (B1) is applied to the surface of the obtained phase difference layer using a wire rod to form a dried film with a thickness of 0.3 μm, thus obtaining a coating layer.

[0487] After drying the coating layer at room temperature for 30 seconds, it was heated for 2 minutes in an atmosphere of 85°C. Then, under an oxygen concentration of less than 1000 ppm, a 90 mW / cm² light bulb manufactured by Fusion UV Systems, INC. was used. 2 The cholesterol-type liquid crystal phase was fixed by irradiating the lamp with 60% output for 6-12 seconds at 60°C, resulting in a cholesterol-type liquid crystal layer B1 with a thickness of 0.3 μm.

[0488] Next, the same process was repeated on the surface of the obtained cholesterol liquid crystal layer B1 using a coating solution (G1) for forming a cholesterol liquid crystal layer, and a cholesterol liquid crystal layer G1 with a thickness of 0.54 μm was stacked.

[0489] Next, the same process was repeated on the surface of the obtained cholesterol liquid crystal layer G1 using a coating solution (R1) for forming a cholesterol liquid crystal layer, and a cholesterol liquid crystal layer R1 with a thickness of 0.36 μm was stacked.

[0490] Thus, a selective reflective layer with three cholesteric liquid crystal layers on the phase retardation layer is obtained. The reflectance spectrum of the selective reflective layer is measured using a spectrophotometer (JASCO Corporation, V-670) to obtain the reflectance spectra that satisfy the necessary conditions (i) to (iii). Figure 2 The graph shown is the reflection spectrum of the reflective film of Example 1.

[0491] Next, the polarization conversion layer forming coating liquid shown in Table 2 is further coated on the surface of the obtained cholesterol-type liquid crystal layer to achieve the target film thickness shown in Table 2, thereby forming a polarization conversion layer and fabricating a reflective film.

[0492] In addition, a polarization conversion layer was formed in the same manner as the formation of the cholesterol-type liquid crystal layer described above.

[0493] [Examples 2-5, Comparative Examples 1-7]

[0494] The structure of the cholesterol-type liquid crystal layer in the light-reflecting layer was changed to the layer structure shown in Table 3 below, and the structure having the polarization conversion layer (or phase difference layer) shown in Table 2 was formed. Otherwise, the reflective film was fabricated in the same manner as in Example 1.

[0495] In addition, regarding Example 3, the cholesterol-type liquid crystal layers G6, R7, and IR4 were formed on a 100 μm thick PET film, after which the PET film was peeled off and sequentially bonded to the cholesterol-type liquid crystal layer B3 formed on the phase retardation layer using OCA (Made by Nichieikako Co., Ltd.: MHM-UVC15, 15 μm thick) to form a selective reflection layer.

[0496] Furthermore, regarding Comparative Examples 1 to 3 and 5, after forming each cholesterol-type liquid crystal layer on a PET film with a thickness of 100 μm, the PET film was peeled off and bonded with OCA (manufactured by Nichieikako Co., Ltd.: MHM-UVC15, 15 μm thick) to form a selective reflective layer.

[0497] Furthermore, regarding Comparative Examples 1 to 3, a 1 / 4 wavelength plate (TEIJINLIMITED: PURE-ACE WR-S, with a delay of 126 nm) was attached to the two sides of the selected reflective layer at angles of 45° and -45° to form the slow axis, respectively, to create a reflective film.

[0498] Furthermore, in Comparative Examples 5-7, a polarization conversion layer was bonded to one side of the selected reflective layer, and a quarter-wavelength plate (made by TEIJIN LIMITED: PURE-ACE WR-S) was bonded to the other side to create a reflective film.

[0499] [Table 3]

[0500]

[0501] [Example 6]

[0502] When forming the cholesterol-type liquid crystal layer, the above-mentioned coating solution C1 for forming the cholesterol-type liquid crystal layer was used to form a cholesterol-type liquid crystal layer C1 with multiple selective reflection center wavelengths as follows. Otherwise, a reflective film was made in the same manner as in Example 1.

[0503] At room temperature, using a wire rod, a cholesterol-type liquid crystal layer forming coating solution C1 is applied to the surface of the phase retardation layer formed on the support (orientation film) in the same manner as in Example 1. The thickness of the dried film after drying is 1.2 μm, thus obtaining the coating layer.

[0504] At room temperature and atmospheric conditions, irradiated with 30 mJ / cm² 2 It was subjected to 365nm UV light and heated for 1 minute in an atmosphere at 85°C. Then, it was irradiated with 60mJ / cm² light at room temperature and in an atmospheric environment. 2 The light was emitted at 365nm UV intensity and heated for 1 minute in an atmosphere at 85°C. Then, under an oxygen concentration below 1000ppm, a 90mW / cm² light bulb manufactured by Fusion UV Systems, INC. was used. 2 The lamp was irradiated with ultraviolet light at 50°C and 60% output for 6-12 seconds to fix the cholesterol-type liquid crystal phase, thus obtaining the cholesterol-type liquid crystal layer C1.

[0505] A polarization conversion layer was formed on the surface of the formed cholesterol-type liquid crystal layer C1 in the same manner as in Example 1 to create a reflective film.

[0506] <Determination of Reflectance Spectra>

[0507] The reflective film is pasted onto the surface of the glass plate, and the black PET film (light absorber) is attached to the back of the glass plate.

[0508] P-polarized and S-polarized light were incident from a direction of 5° relative to the normal direction of the reflective film surface using a spectrophotometer (JASCO Corporation, V-670). The reflectance spectra from 400 nm to 1000 nm were measured. The average reflectance spectra of the measured P-polarized and S-polarized light were calculated (average reflectance spectrum).

[0509] Furthermore, the average values ​​of the reflectance of P-polarized light and S-polarized light have the same meaning as the reflectance of unpolarized light (natural light). That is, the average values ​​of the reflection spectra of P-polarized light and S-polarized light have the same meaning as the reflection spectra of natural light.

[0510] Based on the calculated average values ​​of the reflection spectra of P-polarized and S-polarized light,

[0511] • Calculate the maximum value of natural light reflectance, the difference between the maximum and minimum values ​​of natural light reflectance, and the wavelength bandwidth for the band with wavelengths above 400 nm and below 500 nm.

[0512] • Calculate the maximum value of natural light reflectance, the difference between the maximum and minimum values ​​of natural light reflectance, and the wavelength bandwidth for the band with wavelengths above 500 nm and below 600 nm.

[0513] • Calculate the maximum natural light reflectance and wavelength bandwidth of the band with wavelengths from 600nm to 800nm.

[0514] In addition, the wavelength bandwidth of the band with wavelengths above 400 nm and below 500 nm is the width of the region where the reflectivity is higher than the average of the maximum and minimum reflectivity values ​​of the band with wavelengths above 400 nm and below 500 nm.

[0515] Furthermore, the wavelength bandwidth of the band with wavelengths above 500 nm and below 600 nm is the width of the region where the reflectivity is higher than the average of the maximum and minimum reflectivity values ​​of the band with wavelengths above 530 nm and below 600 nm.

[0516] Furthermore, the wavelength bandwidth above 600nm and below 800nm ​​is the width of the region where the reflectivity is higher than the average of the maximum and minimum reflectivity values ​​of the band with wavelengths between 600nm and 800nm.

[0517] The measurement results are shown in Table 4.

[0518]

[0519] <Windshield Manufacturing>

[0520] The following describes the fabrication of a windshield with the reflective films prepared as described above.

[0521] As the first and second glass plates, a first glass plate with a length of 120mm × width of 100mm and a thickness of 2mm (made by Central Glass Co., Ltd., FL2, visible light transmittance 90%) was prepared.

[0522] Furthermore, as an intermediate membrane, a 0.38 mm thick PVB membrane was prepared by SEKISUI CHEMICAL CO.,LTD.

[0523] Furthermore, the heat-sealing layer is formed as follows.

[0524] <Preparation of the heat seal layer>

[0525] (Coating liquid for heat-sealing layer formation)

[0526] A coating liquid for heat-sealing is prepared by mixing the following components.

[0527] PVB sheet (manufactured by SEKISUI CHEMICAL CO.,LTD., S-LEC film) 5.0 parts by weight

[0528] 90.25 parts by weight of methanol

[0529] 4.75 parts by weight of butanol

[0530] (Formation of the heat-sealing layer)

[0531] After applying a heat-sealing coating liquid to the reflective film (transparent substrate) using a wire rod, the coating is dried and then heated at 50°C for 1 minute to obtain a heat-sealing layer with a thickness of 1 μm.

[0532] In each embodiment and comparative example, the reflective film, the first glass plate, the second glass plate, the intermediate film and the heat sealing layer were stacked to form the structure shown in Table 5 below. After the stack was kept at 90°C and 10 kPa (0.1 atmospheres) for one hour, it was heated in an autoclave (made by Kurihara Manufacturing Co., Ltd.) at 115°C and 1.3 MPa (13 atmospheres) for 20 minutes to remove air bubbles and obtain the windshield.

[0533] [Table 5]

[0534]

[0535] [Evaluation of visible light transmittance]

[0536] Natural light was incident from the second glass plate side at a direction of 0° relative to the normal direction of the second glass plate, and the transmittance spectrum was measured using a spectrophotometer (JASCO Corporation, V-670). According to JIS R3106, transmittance was calculated by multiplying the coefficient corresponding to visibility and the emission spectrum of light source A by the transmittance at each 10 nm wavelength within the range of 380–780 nm, and this transmittance was used for evaluation. The transmittance was evaluated based on the following evaluation criteria.

[0537] Evaluation criteria for transmittance

[0538] • A: 82% or more (when using green glass to form laminated glass, the transmittance is sufficiently higher than 70%)

[0539] • B: 80% or more but less than 82% (when using green glass to form laminated glass, the transmittance exceeds 70%. Compliant with laws and regulations, but with low manufacturing durability)

[0540] • C: Less than 80% (In the case of laminated glass formed with green glass, the transmittance is less than 70%. This does not comply with laws and regulations.)

[0541] [Evaluation of the reflectivity of P-polarized light]

[0542] P-polarized light was incident from the first glass plate side at a direction 65° relative to the normal direction of the first glass plate. The reflectance spectrum of the normally reflected light (at a direction 65° relative to the normal direction on the side of the incident plane opposite to the incident direction) was measured using a spectrophotometer (JASCO Corporation, V-670). At this time, the long side (longitudinal direction) of the reflective film was aligned parallel to the transmission axis of the incident P-polarized light of the spectrophotometer.

[0543] According to JIS R3106, the reflectivity of the projected image is calculated by multiplying the coefficient corresponding to the visibility and the emission spectrum of the D65 light source by the reflectivity for each 10 nm wavelength within the range of 380–780 nm, and this reflectivity is used as the luminance for evaluation. The luminance evaluation is based on the following evaluation criteria.

[0544] Evaluation Criteria for P-Polarized Light Reflectivity

[0545] • A: 25% or more (the image is visible in the P-polarized light reflection system of the HUD, and ghosting is not easily seen)

[0546] • B: Above 20% to less than 25% (The image is visible in the P-polarized light reflection system of the HUD, but ghosting is visible.)

[0547] • C: Less than 20% (In a P-polarized light reflection system of a HUD, the image is not easily seen clearly, and ghosting is clearly visible.)

[0548] [Evaluation of Reflective Tones]

[0549] The reflectance was measured at incident angles of natural light of 5° and 60° using the same method as for transmittance, and the a* and b* of the reflected hue were calculated based on their spectrum.

[0550] Evaluation Criteria for Reflective Tones

[0551] • AA: |a*|≤3 and |b*|≤3 (When projecting white, it appears white)

[0552] • A: |a*|≤5 and |b*|≤5 (except for the part corresponding to AA) (when projected as white, it appears roughly white)

[0553] • B: |a*|≤7 and |b*|≤7 (except for parts corresponding to AA or A) (when projected as white, it appears to have very little hue)

[0554] • C: |a*|≤9 and |b*|≤9 (except for the parts corresponding to AA, A or B) (when projected as white, it appears slightly tinted)

[0555] • D: 9 < |a*| or 9 < |b*| (Other colors are visible when white is projected)

[0556] The results are shown in Table 6.

[0557] [Table 6]

[0558]

[0559] As shown in Table 6, it can be seen that the embodiments of the present invention achieve better results than the comparative examples in terms of visible light transmittance, P-polarized light reflectance (brightness), and reflected hue.

[0560] Comparative Example 1 does not satisfy necessary condition (i), as the natural light reflectance is uniformly high, and therefore the visible light transmittance is low.

[0561] Comparative Example 2 does not satisfy necessary conditions (i) to (iii). The difference between the maximum and minimum values ​​of the natural light reflectance in necessary conditions (i) and (ii) is less than 3%, and the sum of the wavelength bandwidths in necessary condition (iii) is less than 120 nm. Therefore, the visible light transmittance is low, and the P-polarized light reflectance is low.

[0562] Comparative Example 3 does not satisfy necessary conditions (i) to (ii). The difference between the maximum and minimum values ​​of the natural light reflectance in necessary conditions (i) and (ii) is less than 3%, therefore the reflectance of P-polarized light is low.

[0563] Comparative Example 4 does not satisfy necessary condition (i), and the sum of the wavelength bandwidths in necessary condition (iii) is less than 120 nm. Therefore, the result of the reflected hue difference at an incident angle of 5° is obtained.

[0564] Comparing Example 5, which does not satisfy necessary conditions (i) to (ii), we obtain the results of hue difference in reflected light at an incident angle of 5°.

[0565] Comparative Example 6 has high reflectivity under necessary condition (i) and does not meet necessary condition (ii), therefore it has low visible light transmittance and results in hue difference in reflected light at an incident angle of 60°.

[0566] In Comparative Example 7, the sum of the wavelength bandwidths in necessary condition (iii) is less than 120 nm, thus the result of the reflected hue difference at an incident angle of 5° is obtained.

[0567] Based on the comparison between Example 1 and Example 3, it can be seen that the cholesterol-type liquid crystal layer of the reflective layer is preferably in direct contact.

[0568] Based on the comparison between Examples 1 and Examples 4 and 5, it can be seen that the total thickness of the reflective layer is preferably less than 2.0 μm.

[0569] As can be seen from Example 6, the cholesterol-type liquid crystal layer can have multiple selective reflection center wavelengths.

[0570] Based on the above results, the effects of the present invention are clear.

[0571] Industrial availability

[0572] It is ideally suited for use in vehicle head-up display (HUD) systems, etc.

[0573] Symbol Explanation

[0574] 10-Reflective film, 11-Selective reflective layer, 12R, 12G, 12B-Cholesterol-type liquid crystal layer, 14-Polarization conversion layer, 16-Phase reversal layer, 18-Transparent substrate, 20-Head-up display system (HUD), 22-Projector, 24-Windshield, 28-First glass plate, 30-Second glass plate, 36-Intermediate film, 38-Adhesive layer, D-Driver, Y-Up / Down direction.

Claims

1. A reflective film having a selective reflective layer, The selective reflective layer has a cholesterol-type liquid crystal layer formed by fixing a cholesterol-type liquid crystal phase. The selected reflective layer satisfies all of the following necessary conditions (i) to (iii). (i) In the wavelength range of 400 nm and above but less than 500 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths in the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm. (ii) In the wavelength range of 500 nm and above but less than 600 nm, the maximum value of natural light reflectance is 10% to 25%, the difference between the maximum and minimum values ​​of natural light reflectance is 3% or more, and the sum of the wavelength bandwidths in the region above the average of the maximum and minimum values ​​of natural light reflectance is 20 nm to 80 nm. (iii) In the range of wavelengths above 600 nm and below 800 nm, the maximum value of natural light reflectance is 10% to 25%, and the sum of the wavelength bandwidths of the region above the average of the maximum and minimum values ​​of natural light reflectance is above 120 nm.

2. The reflective film according to claim 1, wherein, The selective reflective layer has two or more cholesteric liquid crystal layers with different selective reflective center wavelengths. The cholesterol-type liquid crystal layers are in contact with each other.

3. The reflective film according to claim 1 or 2, wherein, The selective reflective layer comprises a cholesterol-type liquid crystal layer having two or more selective reflective center wavelengths.

4. The reflective film according to claim 1 or 2, wherein, The total thickness of the selective reflective layer is 0.4 μm to 2.0 μm.

5. The reflective film according to claim 1 or 2, which reflects linearly polarized light.

6. The reflective film according to claim 1 or 2, wherein it sequentially comprises a phase difference layer, the selective reflection layer and the polarization conversion layer.

7. The reflective film according to claim 6, wherein, The polarization conversion layer is formed by fixing the helical alignment structure of the liquid crystal compound. The pitch number x of the spiral orientation structure in the polarization conversion layer and the film thickness y of the polarization conversion layer satisfy all of the following equations (a) to (c), where the unit of film thickness y is μm. 0.1≤x≤1.0···Equation (a), 0.5≤y≤3.0···Equation (b) 3000≤(1560×y) / x≤50000···Equation (c).

8. A windshield comprising, in sequence, a first glass plate, a reflective film according to any one of claims 1 to 7, and a second glass plate.

9. The windshield according to claim 8, wherein, The first glass plate and the second glass plate are curved glass. The reflective film and the second glass plate are disposed on the convex side of the first glass plate.

10. The windshield according to claim 9, wherein, The reflective film has a polarization conversion layer. The polarization conversion layer and the selective reflection layer are sequentially arranged from the convex side of the first glass plate.

11. The windshield according to claim 9 or 10, wherein, The reflective film has a phase retardation layer. The phase retardation layer is disposed between the selective reflection layer and the second glass plate. The frontal delay of the phase retardation layer at a wavelength of 550 nm is 50 nm to 160 nm, and when the following direction is set to 0°, the angle of the slow axis of the phase retardation layer is 10° to 50° or -50° to -10°, the direction being the direction corresponding to the vertical direction above the surface of the first glass plate when the windshield is installed on the vehicle.

12. The windshield according to claim 9 or 10, wherein, The reflective film has a transparent substrate. The transparent substrate is disposed on the side of the second glass plate.

13. The windshield according to claim 12, wherein, The transparent substrate contains an ultraviolet absorber.

14. The windshield according to any one of claims 8 to 10, wherein an intermediate film is provided between the first glass plate and the reflective film.

15. The windshield according to any one of claims 8 to 10, wherein a heat-sealing layer is provided between the reflective film and the second glass plate.

16. A head-up display system, comprising: The windshield according to any one of claims 9 to 15; and The projector projects light onto the first glass panel side of the windshield.

17. The head-up display system according to claim 16, wherein, The projector illuminates p-polarized projection light.

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