Optical film, windshield glass, and head-up display system

Abstract

The present invention provides: an optical film that, when used in combination with a glass sheet as windshield glass in a head-up display system, suppresses double images and can maintain the visibility of scenery even when light is radiated onto the windshield glass; windshield glass; and a head-up display system. This optical film comprises high-refractive-index regions and low-refractive-index regions that alternate in one in-plane direction of the optical film. In a cross-section aligned with the one in-plane direction and cut in a thickness direction, the high-refractive-index regions and the low-refractive-index regions both extend in a direction that is oblique with respect to a normal direction of the surface of the optical film. An angle formed by the normal direction and the direction of extension of the high-refractive-index regions and an angle formed by the normal direction and the direction of extension of the low-refractive-index regions are both in the range 36°–50°. The haze of the optical film measured in the normal direction is 2.0% or less.

Description

Optical film, windshield glass, head-up display systems

[0001] The present invention relates to an optical film, a windshield glass, and a head-up display system.

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

[0003] Patent Document 1 describes a head-up display system that has a reflective layer and a polarization conversion layer made up of a retardation layer and a cholesteric liquid crystal layer and is capable of reflecting P-polarized light. The windshield glass that constitutes the head-up display system is required to prevent double images from being seen. In the method of Patent Document 1, the head-up display system directs P-polarized light into the windshield glass, thereby reducing the reflectance at the air interface on the outside of the vehicle of the windshield glass and making double images less visible.

[0004] International Publication No. 2020 / 080355

[0005] In recent years, there has been a trend toward steeper windshield glass in order to further reduce vehicle air resistance. In other words, the windshield glass is positioned more horizontally. It has been discovered that in head-up display systems that include such steeper windshield glass, the angle of incidence of projected light onto the windshield glass becomes steeper (larger), which can lead to the problem of double images being more likely to occur. This problem is particularly pronounced when the projected light is P-polarized. Furthermore, in head-up display systems, it is anticipated that headlight light from oncoming vehicles may be irradiated onto the windshield glass, and it is also required that the driver be able to easily see the background outside the vehicle even in such cases.

[0006] In view of the above circumstances, an object of the present invention is to provide an optical film that, when combined with a glass plate and applied to a head-up display system as a windshield glass, suppresses the occurrence of double images and ensures background visibility even when light is irradiated onto the windshield glass. Another object of the present invention is to provide a windshield glass and a head-up display system.

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

[0008] (1) An optical film having high refractive index regions and low refractive index regions alternately along one direction in the plane of the optical film, in a cross section cut in the thickness direction along one direction, both the high refractive index regions and the low refractive index regions extend in a direction inclined with respect to the normal direction to the surface of the optical film, the angle between the normal direction and the extending direction of the high refractive index regions and the angle between the normal direction and the extending direction of the low refractive index regions are both 36 to 50 degrees, and the haze measured from the normal direction of the optical film is 2.0% or less. (2) The optical film according to (1), wherein the thickness d of the optical film is 1 to 50 μm. (3) The optical film according to (1) or (2), wherein the difference Δn between the refractive index of the high refractive index regions and the refractive index of the low refractive index regions is 0.005 to 0.5. (4) The optical film according to any one of (1) to (3), wherein the product of the thickness d of the optical film and the difference Δn between the refractive index of the high refractive index region and the refractive index of the low refractive index region is 0.20 to 0.30 μm. (5) The optical film according to any one of (1) to (4), wherein, in the one direction, the width of the high refractive index region at the surface of the optical film and the width of the low refractive index region at the surface of the optical film are both 1.0 to 3.0 μm. (6) A windshield glass comprising a first glass plate, the optical film according to any one of (1) to (5), an interlayer film, and a second glass plate. (7) The windshield glass according to (6), further comprising a reflective layer on the side of the second glass plate opposite to the interlayer film side. (8) A head-up display system comprising the windshield glass according to (6) or (7) and a projector that projects projection light onto the windshield glass. (9) The head-up display system according to (8), wherein the projected light is P-polarized light and the angle of incidence of the projected light on the windshield glass is 60 to 75 degrees.

[0009] According to the present invention, it is possible to provide an optical film that, when combined with a glass plate to form a windshield glass and applied to a head-up display system, suppresses the occurrence of double images and ensures background visibility even when light is irradiated onto the windshield glass. Furthermore, the present invention can provide a windshield glass and a head-up display system.

[0010] It is a schematic diagram of a conventional head-up display system. It is a schematic diagram of a head-up display system of the present invention. It is a plan view of an example of an optical film. It is a cross-sectional view of an example of an optical film. It is a schematic diagram for explaining a method of manufacturing an optical film.

[0011] The optical film, windshield glass, and head-up display system of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings. The drawings described below are merely illustrative for explaining the present invention, and the present invention is not limited to these drawings. In the following, the term "to" indicating a numerical range includes the values ​​written on both sides. For example, when ε1 is between α1 and β1, the range of ε1 includes α1 and β1, and expressed mathematically as α1≦ε1≦β1. Furthermore, the term "same" includes a generally accepted error range in the relevant technical field, and terms such as "overall" also include generally accepted error ranges in the relevant technical field.

[0012] Unless otherwise specified, the term "light" refers to visible light and natural light (unpolarized). Visible light is electromagnetic light with wavelengths visible to the human eye, and typically refers to light in the wavelength range of 380 to 780 nm. Invisible light is light in the wavelength range of less than 380 nm or greater than 780 nm. Furthermore, although not limited thereto, within visible light, light in the wavelength range of 420 to 490 nm is blue (B) light, light in the wavelength range of 495 to 570 nm is green (G) light, and light in the wavelength range of 620 to 750 nm is red (R) light.

[0013] The "visible light transmittance" is the A-light source visible light transmittance defined in JIS (Japanese Industrial Standards) R 3212:2015 (Test Methods for Automotive Safety Glass). That is, the transmittance is determined by measuring the transmittance at each wavelength in the wavelength range of 380 to 780 nm using a spectrophotometer with an A-light source, and multiplying the transmittance at each wavelength by a weighting coefficient obtained from the wavelength distribution and wavelength interval of the CIE (Commission Internationale de l'Eclairage) photopic standard relative luminosity factor, and calculating a weighted average. When simply referring to "reflected light" or "transmitted light," this term is used to include scattered light and diffracted light.

[0014] P-polarized light refers to polarized light that vibrates in a direction parallel to the plane of incidence of light, while S-polarized light refers to polarized light that vibrates in a direction perpendicular to the plane of incidence of light. The plane of incidence is perpendicular to the reflecting surface (such as the surface of a windshield glass) and refers to the plane that contains the incident and reflected light rays. In P-polarized light, the vibration plane of the electric field vector is parallel to the plane of incidence, while in S-polarized light, the vibration plane of the electric field vector is perpendicular to the plane of incidence.

[0015] The in-plane retardation (in-plane phase difference) is a value measured using an AxoScan manufactured by Axometrics. Unless otherwise specified, the measurement wavelength is 550 nm. The in-plane retardation is measured by irradiating light with a wavelength within the visible light wavelength range in the normal direction of the film (normal direction of the surface of the retardation layer).

[0016] "Projection image" means an image that is not a view of the surroundings, such as the front, but is based on the projection of light from the projector used. The projected image is perceived by the observer as a virtual image that appears to appear beyond the windshield glass. The projected image may be a monochromatic image, a multicolor image with two or more colors, or a full-color image.

[0017] As described below, the optical film of the present invention has characteristics in that it has high refractive index regions and low refractive index regions extending along a direction inclined at a predetermined angle relative to the normal direction of the surface of the optical film, and that its haze is within a predetermined range.

[0018] First, a phenomenon in which double images tend to occur in a conventional head-up display system will be described with reference to FIG. 1 . The head-up display system 100 shown in FIG. 1 is an in-vehicle head-up display system that includes a windshield 102 and a projector 104 that emits projection light onto the windshield 102. Recently, there has been a trend toward steeper windshield inclinations. In other words, windshields are positioned more horizontally. Therefore, as shown by the solid line in FIG. 1 , the angle of incidence of the projection light emitted from the projector 104 onto the windshield 102 is increasing. In such a case, as shown by the dashed line in FIG. 1 , a portion of the projection light emitted from the projector 104 is not reflected by the windshield 102 but enters the windshield 102, is then reflected within the windshield 102, and is ultimately viewed by an observer OB. The presence of such light indicated by the dashed line causes double images to occur. One method for suppressing the occurrence of double images as described above is to use a known light-diffusing film, but when such a light-diffusing film is used, the windshield glass turns white when light from the headlights of an oncoming vehicle is irradiated onto the windshield glass, making it difficult for the driver to see the background outside the vehicle. As will be described later, the present invention solves the above problem.

[0019] FIG. 2 shows an example of a head-up display system according to the present invention. The head-up display system 10 shown in FIG. 2 is an in-vehicle head-up display system that includes a windshield 12 and a projector 14 that emits projection light onto the windshield 12. The windshield 12 includes, in this order, a first glass plate 20, an optical film 22, an intermediate film 24, a second glass plate 26, and a reflective layer 28. In the head-up display system 10 shown in FIG. 2, a portion of the projection light emitted from the projector 14 is reflected by the reflective layer 28 in the windshield 12, as shown by the solid line, and is observed by an observer OB. As with a typical head-up display system, in the example shown in FIG. 2, the observer OB observes the image projected onto the windshield 12 as a virtual image through the windshield 12.

[0020] In Fig. 2, projector 14 emits P-polarized projection light, and windshield glass 12 reflects the P-polarized light. The present invention is not limited to the embodiment shown in Fig. 1, and may be an embodiment in which the projector emits S-polarized projection light, and the windshield glass reflects the S-polarized light. The angle of incidence when projecting light from projector 14 onto windshield glass 12 is not particularly limited, but in the present invention, it is preferably 60 to 75°, more preferably 65 to 75°, and even more preferably 70 to 75°.

[0021] In the head-up display system 10 shown in FIG. 2 , a portion of the projection light emitted from the projector 14 is reflected toward the observer OB by the reflective layer 28, as indicated by the solid line. Meanwhile, a portion of the projection light emitted from the projector 14 travels into the windshield glass 12 without being reflected by the reflective layer 28, as indicated by the dashed line in FIG. 2 . If an optical film 22 is included in the windshield glass 12, the optical film 22, which has alternating high-refractive-index regions and low-refractive-index regions, functions as a diffractive element, changing the direction of travel of light incident on the optical film 22. As a result, the light incident on the windshield glass 12 is repeatedly totally reflected within the windshield glass 12, and does not become exiting light that causes double images as shown in FIG. 1 , thereby suppressing the occurrence of double images. Note that the optical film 22 diffracts light in various directions, and FIG. 2 shows light traveling in the direction indicated by the dashed line as an example. Even light traveling in a direction other than that indicated by the dashed line in FIG. 2 does not travel toward the observer OB, thereby suppressing the occurrence of double images. Furthermore, since the optical film 22 has a haze measured from the normal direction of 2% or less, it is less likely to whiten when irradiated with light, thereby ensuring background visibility. The magnitude of the haze can be adjusted by adjusting the sizes of the high refractive index regions and the low refractive index regions. More specifically, the haze can be adjusted, for example, by adjusting the widths of the high refractive index regions and the low refractive index regions in the direction in which the high refractive index regions and the low refractive index regions are aligned on the optical film surface, as described below. In addition to the above widths, the haze can also be adjusted by the thickness of the optical film and the refractive index difference between the high refractive index regions and the low refractive index regions.

[0022] Hereinafter, each component of the head-up display system 10 will be described in detail. First, the optical film 22, which is a characteristic feature of the head-up display system 10, will be described in detail.

[0023] <Optical Film> The optical film 22 is a component included in the windshield glass 12, and has the function of changing the traveling direction of light incident on the optical film 22, as described above in FIG. 2. FIG. 3 is a plan view of the optical film 22, and FIG. 4 is a cross-sectional view of the optical film shown in FIG. 3. Note that FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3. In FIG. 3, direction X and direction Y indicate the orientations of two coordinate axes that are perpendicular to each other on the observation surface. Direction X and direction Y correspond to in-plane directions of the optical film. In FIG. 4, direction X and direction Z indicate the orientations of two coordinate axes that are perpendicular to each other on the observation surface. Direction Z corresponds to the thickness direction of the optical film.

[0024] As shown in FIG. 3 , the optical film 22 has rectangular high-refractive-index regions 30 and rectangular low-refractive-index regions 32 alternately arranged along one in-plane direction (the X-axis direction in FIG. 3 ) of the optical film. The rectangular high-refractive-index regions 30 and the rectangular low-refractive-index regions 32 extend in a direction perpendicular to the above-mentioned direction (the Y-axis direction in FIG. 3 ). The refractive index of the high-refractive-index regions 30 is greater than that of the low-refractive-index regions 32. Furthermore, as shown in FIG. 4 , in a cross section cut in the thickness direction along the above-mentioned direction, both the high-refractive-index regions 30 and the low-refractive-index regions 32 extend in a direction inclined with respect to the normal direction to the surface of the optical film (the Z-direction in FIG. 4 ). More specifically, as shown in FIG. 4 , in the optical film 22, plate-shaped high-refractive-index regions 30 and plate-shaped low-refractive-index regions 32 are alternately arranged adjacent to each other along one direction (the X-axis direction in FIG. 4 ). That is, the high-refractive-index regions 30 and the low-refractive-index regions 32 are arranged so that their respective principal surfaces face each other. As shown in FIG. 4, in a cross section cut in one direction in the thickness direction, the high refractive index regions 30 and the low refractive index regions 32 both extend from one surface to the other surface of the optical film.

[0025] As described above, the high refractive index regions 30 and the low refractive index regions 32 both extend in a direction inclined with respect to the normal direction (Z direction in FIG. 4 ) of the surface of the optical film. More specifically, the angle AH between the normal direction and the direction in which the high refractive index regions 30 extend, and the angle AL between the normal direction and the direction in which the low refractive index regions 32 extend, are both 36 to 50°. In particular, the angles AH and AL are preferably 38 to 50°, and more preferably 40 to 48°, in order to further suppress the occurrence of double images. The angles AH and AL are calculated as follows. First, the optical film 22 is cut in the thickness direction along one direction in which the high refractive index regions 30 and the low refractive index regions 32 are alternately arranged, and the exposed cross section is observed with an optical microscope. A line is drawn connecting the center position of the observed high refractive index region 30 on one surface of the optical film 22 (the center position of the side that constitutes the high refractive index region 30 on one surface of the optical film 22) and the center position of the other surface of the optical film 22 (the center position of the side that constitutes the high refractive index region 30 on the other surface of the optical film 22), and the angle AH is the angle formed by the obtained line and the normal direction. Also, a line is drawn connecting the center position of the observed low refractive index region 32 on one surface of the optical film 22 (the center position of the side that constitutes the low refractive index region 32 on one surface of the optical film 22) and the center position of the other surface of the optical film 22 (the center position of the side that constitutes the low refractive index region 32 on the other surface of the optical film 22), and the angle AL is the angle formed by the obtained line and the normal direction.

[0026] The haze measured from the normal direction of the optical film 22 is 2.0% or less. In particular, 1.5% or less is more preferable, and 1.0% or less is even more preferable, since this provides better background visibility even when light is irradiated onto the windshield glass. The lower limit is not particularly limited, and is often 0% or more, and more often 0.1% or more. The haze is measured as follows: Using a D65 light source, white light is incident from the normal direction of the optical film 22, and the haze is measured with a turbidity meter (NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0027] The difference Δn between the refractive index of the high refractive index region 30 and the refractive index of the low refractive index region 32 is not particularly limited, but is preferably 0.005 to 0.5, more preferably 0.008 to 0.10, and even more preferably 0.01 to 0.05, in order to further suppress the occurrence of double images. The refractive index is measured at a wavelength of 550 nm. The method for measuring the difference Δn is not particularly limited, and known methods can be used. To calculate the difference Δn, the components contained in the high refractive index region 30 and the low refractive index region 32 may be analyzed, and the refractive indices of the high refractive index region 30 and the low refractive index region 32 may be calculated from the refractive indices and composition ratios of the components contained in each region, and the difference Δn may be determined. For example, the components contained in the high refractive index region 30 and the low refractive index region 32 may be analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the refractive index of each region may be calculated from the refractive indices and composition ratios of the components themselves.

[0028] The refractive index of the high refractive index region 30 is not particularly limited, but is preferably 1.50 to 1.65, and more preferably 1.52 or more and less than 1.62, in order to further suppress the occurrence of double images. The refractive index of the low refractive index region 32 is not particularly limited, but is preferably 1.45 to 1.55, and more preferably 1.48 or more and less than 1.52, in order to further suppress the occurrence of double images.

[0029] The thickness d of the optical film 22 is not particularly limited, and is preferably 1 to 50 μm, more preferably 2 to 35 μm, and even more preferably 3 to 20 μm, in order to further suppress the occurrence of double images. The thickness d of the optical film 22 is a value obtained by measuring the thickness of the optical film at any 10 points on a cross section cut in the thickness direction along the one direction and arithmetically averaging the measured values.

[0030] The product Δnd of the thickness d of the optical film 22 and the difference Δn between the refractive index of the high refractive index region 30 and the refractive index of the low refractive index region 32 is not particularly limited, but is preferably 0.10 to 0.80 μm, and more preferably 0.20 to 0.30 μm, in that the occurrence of double images is further suppressed.

[0031] The width WH of the high refractive index region 30 in one direction (X direction in FIG. 3) in which the high refractive index region 30 and the low refractive index region 32 are alternately arranged on the surface of the optical film 22 shown in FIG. 3 is not particularly limited, but is preferably 0.5 to 8.0 μm, and more preferably 1.0 to 3.0 μm, in order to further suppress rainbow unevenness. The width WL of the low refractive index region 32 in one direction (X direction in FIG. 3) in which the high refractive index region 30 and the low refractive index region 32 are alternately arranged on the surface of the optical film 22 shown in FIG. 3 is not particularly limited, but is preferably 0.5 to 8.0 μm, and more preferably 1.0 to 3.0 μm, in order to further suppress rainbow unevenness.

[0032] In FIG. 2 , the optical film 22 is disposed over the entire surface of the first glass plate 20, but the present invention is not limited to this embodiment, and the optical film 22 may be disposed over only a partial area of ​​the first glass plate 20.

[0033] The material constituting the optical film 22 is not particularly limited, and known materials can be used. Examples of such materials include organic and inorganic materials, with organic materials being preferred and polymers being more preferred. The type of polymer is not particularly limited, and known polymers can be used. As described above, polymers are preferred as the materials contained in the high refractive index regions 30 and the low refractive index regions 32 of the optical film 22. Examples of polymers include (meth)acrylic resins, polyurethane resins, polyamide resins, polyester resins, epoxy resins, polyacetal resins, polyhydroxystyrene resins, polyimide resins, polybenzoxazole resins, and polysiloxane resins, with (meth)acrylic resins being preferred. A (meth)acrylic resin is a resin containing repeating units derived from a (meth)acrylate monomer. The term "(meth)acrylate" is used to mean "either one or both of acrylate and methacrylate." The term "(meth)acrylic" is used to mean "either one or both of acrylic and methacrylic." When both the high refractive index region 30 and the low refractive index region 32 contain a polymer, the type of repeating unit in the polymer contained in the high refractive index region 30 may be different from or the same as the type of repeating unit in the polymer contained in the low refractive index region 32. When the same type of repeating unit is contained in both the polymer contained in the high refractive index region 30 and the polymer contained in the low refractive index region 32, it is preferable that the contents of the repeating units are different between the two.

[0034] The method for manufacturing the optical film 22 is not particularly limited, and known methods can be employed. Among these, a method using two types of monomers with different polymerization rates and different refractive indices is preferred. The steps of this method are described in detail below. First, a composition containing two types of monomers with different polymerization rates and different refractive indices is prepared, and a coating film is formed using the resulting composition. The coating film corresponds to a precursor layer of the optical film. A mask with a predetermined opening is placed on the precursor layer, and light is incident on the mask from an oblique direction to polymerize the monomers. More specifically, as shown in FIG. 5 , a mask 42 is placed on a precursor layer 40 containing two types of monomers with different polymerization rates and different refractive indices, and the precursor layer 40 is tilted to allow light to be incident from the direction indicated by the white arrow. Polymerization of the monomers proceeds in the areas irradiated with the incident light, with the monomer with the faster polymerization rate polymerizing first. Therefore, the monomer with the faster polymerization rate is more concentrated in the irradiated areas, creating a monomer concentration gradient, and the monomer with the slower polymerization rate is concentrated in the areas not irradiated with light. Thereafter, a curing process is performed by irradiating the entire surface of the precursor layer 40 from the direction opposite to the mask 42 side of the precursor layer 40, thereby forming an optical film including a high refractive index region containing a large amount of components derived from a monomer with a high refractive index and a low refractive index region containing a large amount of components derived from a monomer with a low refractive index.

[0035] The two types of monomers used in the above method are not particularly limited as long as they have different polymerization rates and different refractive indices. The two types of monomers are preferably (meth)acrylate monomers.

[0036] The composition for forming the precursor layer may contain a polymerization initiator. The type of polymerization initiator is not particularly limited, and known polymerization initiators can be used, with photopolymerization initiators being preferred.

[0037] The angle of incidence of light when the light is incident obliquely on the precursor layer 40 is not particularly limited, and an optimum angle is appropriately selected so that the above-mentioned angles AH and AL are within a predetermined range. The type of light used is not particularly limited, and ultraviolet light is preferred.

[0038] As described above, the curing process performed after the light is incident on the precursor layer 40 from an oblique direction is preferably a light irradiation process, but a thermal curing process may also be performed. Various light sources such as infrared light, visible light, and ultraviolet light can be used as the light source for curing, but ultraviolet light is preferred. Furthermore, ultraviolet light may be irradiated while heating during curing, or ultraviolet light may be irradiated through a filter that transmits only specific wavelengths.

[0039] <Projector> The configuration of the projector 14 is not particularly limited as long as it can emit projection light onto the windshield glass 12, and any known projector can be used.

[0040] The projection light emitted by the projector 14 is preferably P-polarized light. The projector 14 may have a polarizer therein in order to emit P-polarized projection light.

[0041] Examples of the projector 14 include an LCOS (Liquid Crystal on Silicon) projector, a laser projector, and a liquid crystal projector (liquid crystal display device).

[0042] <Windshield Glass> As described above, the windshield glass 12 includes the first glass plate 20, the optical film 22, the intermediate film 24, the second glass plate 26, and the reflective layer 28, in this order.

[0043] When the windshield glass 12 is used in a vehicle, curved glass is often used as the first glass sheet 20 and the second glass sheet 26. There are no restrictions on the visible light transmittance of the windshield glass 12, but a higher value is preferable. The visible light transmittance of the windshield glass 12 is preferably 70% or more, more preferably greater than 70%, even more preferably 75% or more, and particularly preferably 80% or more. The above-mentioned visible light transmittance is preferably satisfied at all positions on the windshield glass 12, and is particularly preferably satisfied at the position where the reflective layer 28 is present.

[0044] (First Glass Sheet and Second Glass Sheet) Glass sheets generally used for windshield glass can be used for the glass sheets such as the first glass sheet 20 and the second glass sheet 26. For example, glass sheets having a visible light transmittance of 80% or less, such as 73% or 76%, such as green glass with high heat insulation properties, may be used.

[0045] There are no particular limitations on the thickness of the first glass plate 20 and the second glass plate 26, but it is sufficient if it is about 0.5 to 5.0 mm, and preferably 1.0 to 3.0 mm. The materials or thicknesses of the first glass plate 20 and the second glass plate 26 may be the same or different.

[0046] (Interlayer Film) The interlayer film 24 prevents glass from penetrating into the vehicle interior and scattering in the event of an accident, and in the example shown in FIG. 2 , it bonds the optical film 22 and the second glass plate 26 together.

[0047] Any known interlayer film can be used as the interlayer film 24 (interlayer film sheet). For example, a resin film containing a resin selected from the group consisting of polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, and chlorine-containing resin can be used. The above-mentioned resin is preferably the main component of the interlayer film. Here, "main component" refers to a component that accounts for 50% or more by mass of the interlayer film 24.

[0048] Of the above resins, polyvinyl butyral or ethylene-vinyl acetate copolymer is preferred, and polyvinyl butyral is more preferred. The resin is preferably a synthetic resin. Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol with butyraldehyde. The degree of acetalization of the above polyvinyl butyral is preferably 40 to 85%, more preferably 60 to 75%.

[0049] The thickness of the interlayer 24 is not particularly limited, and may be set in accordance with the material used, similar to that of interlayers in known windshield glass.

[0050] (Reflective Layer) The configuration of the reflective layer 28 is not particularly limited as long as it has the function of reflecting the projection light emitted from the projector 14. In particular, it is preferable that the reflective layer 28 includes a cholesteric liquid crystal layer, in that the effects of the present invention are more excellent.

[0051] The cholesteric liquid crystal layer is a layer in which liquid crystal compounds are fixed in a helical oriented state of a cholesteric liquid crystal phase, and reflects light with a selective reflection center wavelength corresponding to the pitch of the helical structure and transmits light in other wavelength ranges. The cholesteric liquid crystal layer also exhibits selective reflection for either left- or right-handed circularly polarized light at a specific wavelength.

[0052] The reflective layer 28 may be a cholesteric liquid crystal layer that reflects right-handed circularly polarized light or a cholesteric liquid crystal layer that reflects left-handed circularly polarized light. Alternatively, the reflective layer 28 may include a cholesteric liquid crystal layer that reflects right-handed circularly polarized light and a cholesteric liquid crystal layer that reflects left-handed circularly polarized light. The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the reflective layer 28 and / or the type of chiral agent added. The reflective layer 28 may include multiple cholesteric liquid crystal layers with different selective reflection center wavelengths. For example, the reflective layer 28 may include a cholesteric liquid crystal layer having a selective reflection center wavelength in the wavelength range of red light, a cholesteric liquid crystal layer having a selective reflection center wavelength in the wavelength range of green light, and a cholesteric liquid crystal layer having a selective reflection center wavelength in the wavelength range of blue light.

[0053] (Retardation Layer) The windshield glass 12 may further include a retardation layer. The retardation layer is preferably disposed on the side of the reflective layer 28 opposite to the second glass plate 26 side.

[0054] When the retardation layer has a function of converting P-polarized light irradiated from the projector 14 into circularly polarized light, the retardation layer is preferably configured to give an in-plane retardation of λ / 4, and may be configured to give an in-plane retardation of 3λ / 4. The retardation layer may be disposed such that the angle of the slow axis thereof is oriented in a direction that converts incident linearly polarized light into circularly polarized light.

[0055] In this case, the in-plane retardation of the retardation layer at a wavelength of 550 nm is preferably in the range of 100 to 450 nm, more preferably in the range of 120 to 200 nm or 300 to 400 nm.

[0056] The type of retardation layer is not particularly limited and can be appropriately selected according to purpose.For example, retardation layer can be a stretched polycarbonate film, a stretched norbornene polymer film, a transparent film containing and oriented inorganic particles having birefringence such as strontium carbonate, a thin film obtained by obliquely depositing an inorganic dielectric on a support, a film obtained by uniaxially aligning a polymerizable liquid crystal compound and fixing the orientation, and a film obtained by aligning a liquid crystal compound and fixing the orientation.

[0057] The thickness of the retardation layer is not particularly limited, but is preferably 0.2 to 300 μm, more preferably 0.5 to 150 μm.

[0058] (Polarization Conversion Layer) The windshield glass 12 may further include a polarization conversion layer. The polarization conversion layer is preferably disposed between the second glass plate 26 and the reflective layer 28. The polarization conversion layer exhibits optical rotation and birefringence for visible light and converts the polarization state of incident light. The polarization conversion layer is preferably a layer in which a helical structure of a liquid crystal compound is fixed. In particular, the polarization conversion layer is preferably a layer in which a helical structure of a liquid crystal compound is fixed, and the pitch number x of the helical structure and the film thickness y (unit: μm) of the polarization conversion layer preferably satisfy all of the following relational expressions (a) to (c): 0.1≦x≦1.0 (equation (a)); 0.5≦y≦3.0 (equation (b)); and 3000≦(1560×y) / x≦50000 (equation (c)). Note that one pitch of the helical structure of the liquid crystal compound is one turn of the helix of the liquid crystal compound. That is, the pitch number is defined as 1 when the director of the helically aligned liquid crystal compound (the long axis direction in the case of a rod-like liquid crystal) rotates 360°.

[0059] When the liquid crystal compound has a helical structure that satisfies the relational expressions (a) to (c), the polarization conversion layer exhibits optical rotation and birefringence for visible light.

[0060] The pitch number x of the helical structure of the polarization conversion layer is more preferably 0.1 to 0.8, the film thickness y is more preferably 0.6 to 2.6 μm, and "(1560×y) / x" is more preferably 5000 to 13000.

[0061] (Heat Seal Layer) The windshield glass 12 may further include a heat seal layer. The heat seal layer is preferably disposed between the first glass plate 20 and the optical film 22. The type of heat seal layer is not particularly limited, and any known coating-type adhesive can be used as long as it can ensure the transparency required for the windshield glass 12 and can bond the first glass plate 20 and the optical film 22 with the required adhesive strength. The heat seal layer may be the same as the interlayer film, such as PVB.

[0062] The heat seal layer may be formed from an adhesive. The adhesive may be a hot-melt type, a heat-curing type, a light-curing type, a reaction-curing type, or a pressure-sensitive adhesive type that does not require curing, depending on the curing method. The heat seal layer may be formed using a highly transparent adhesive transfer tape (OCA tape).

[0063] The windshield glass 12 may include other components in addition to the various components described above. For example, the windshield glass 12 may have adhesive layers disposed between the components to improve adhesion between the components. Known pressure-sensitive adhesive layers and adhesive layers can be used as the adhesive layers. The windshield glass 12 may also include a substrate. Examples of the substrate include a resin substrate.

[0064] <Uses> The head-up display system of the present invention can be used in a variety of applications, including, for example, an in-vehicle head-up display system.

[0065] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following examples.

[0066] <Preparation of Optical Film> A composition was prepared by mixing 100 parts by mass of A-LEN-10 (hereinafter, see structural formula), 100 parts by mass of EBECRYL270 (hereinafter, see structural formula), and 10 parts by mass of Irgacure1173 (hereinafter, see structural formula).

[0067] A-LEN-10 (see structural formula below)

[0068]

[0069] EBECRYL270 (see structural formula below)

[0070]

[0071] Irgacure1173 (see structural formula below)

[0072]

[0073] The composition obtained above was applied with an applicator to the adhesive layer side of a polyethylene terephthalate (PET) substrate (Toyobo, A4100, film thickness 100 μm) to form a precursor layer. Next, a line-shaped mask (200 mm × 400 mm) with a horizontal width (5 μm) was prepared, and the mask was attached to the precursor layer using a roller. The masked precursor layer was then tilted and fixed as shown in Figure 5. Subsequently, ultraviolet light was irradiated for 6 seconds from an electrodeless lamp "D Bulb" manufactured by Fusion UV Systems, Inc., from a direction obliquely 70° from the normal direction of the mask (a direction tilted 70° from the normal direction) (irradiation dose 40 mJ / cm ２ Next, ultraviolet light was irradiated from the PET substrate side in the normal direction of the PET substrate (irradiation dose 600 mJ / cm ２ ), a periodic structure having alternating plate-shaped high refractive index regions and plate-shaped low refractive index regions was formed. Thereafter, the mask was peeled off to obtain an optical film (thickness: 30 μm).

[0074] Next, the optical film was cut with a razor. The cutting was performed along a direction in which the high refractive index regions and the low refractive index regions were alternately arranged, and a cross section cut along the direction in the thickness direction was exposed and observed with an optical microscope. The observation confirmed the formation of a structure in which high refractive index regions and low refractive index regions were alternately arranged, extending in a direction inclined at 44° with respect to the normal direction of the optical film surface. The high refractive index regions and low refractive index regions were observed as bright and dark areas under the optical microscope. Both the high refractive index regions and the low refractive index regions extended from one surface to the other surface of the optical film (see FIG. 4 ). On the surface of the optical film (the surface opposite the PET substrate), the width of the high refractive index region (width WH in FIG. 3 ) and the width of the low refractive index region (width WL in FIG. 3 ) were each 5 μm. The refractive index differences Δn between the high refractive index regions and the high refractive index regions were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Specifically, the components in the high refractive index region and the low refractive index region were analyzed by TOF-SIMS, and the representative structure (C １２ H ９ O － ) and a representative structure of EBECRYL270, a low refractive index material (CNO － ) were compared, and the composition ratio of the high refractive index material and the low refractive index material was analyzed from the intensity ratio, and the refractive indices of the high refractive index region and the low refractive index region were calculated. The refractive index of the high refractive index region was 1.53, and the refractive index of the low refractive index region was 1.51, and the refractive index difference Δn was 0.02. In addition, the haze of the optical film was measured using a turbidity meter (NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.) with white light incident from the normal direction of the film using a D65 light source, and it was confirmed that the haze was 1.5%. In measuring the haze of the optical film, a laminate of the optical film and a PET substrate was used as the measurement object, and the haze value of the PET substrate alone was taken into account from the obtained measurement value to calculate the haze of the optical film alone.

[0075] <Formation of Reflective Layer> A cellulose acylate film with a thickness of 40 μm was prepared by the same preparation method as in Example 20 of WO 2014 / 112575. UV-531 manufactured by Teisei Chemical Industry Co., Ltd. was added to this cellulose acylate film as an ultraviolet absorber. The amount added was 3 phr (per hundred resin). The prepared cellulose acylate film was passed through a dielectric heating roll at a temperature of 60° C., and the film surface temperature was raised to 40° C. Thereafter, an alkaline solution having the composition shown below was applied to one side of the film using a bar coater in an amount of 14 mL / m ２ The coating was then allowed to stand for 10 seconds under a steam-type far-infrared heater (manufactured by Noritake Co., Ltd.) heated to 110°C. Next, pure water was applied at a rate of 3 mL / m using the same bar coater. ２ The film was then washed with water using a fountain coater and then dried with an air knife three times, and then allowed to stay in a drying zone at 70°C for 5 seconds to dry, thereby preparing a saponified cellulose acylate film. The in-plane retardation of the saponified cellulose acylate film was measured with an AxoScan and found to be 1 nm.

[0076] Composition of alkaline solution: Potassium hydroxide 4.7 parts by mass; Water 15.7 parts by mass; Isopropanol 64.8 parts by mass; Surfactant (C １６ H ３３ O (CH ２ CH ２ O) １０ H) 1.0 part by mass Propylene glycol 14.9 parts by mass

[0077] A coating solution for forming an alignment layer having the composition shown below was applied to the saponified surface of a saponified cellulose acylate film (transparent support) at a rate of 24 mL / m using a wire bar coater.２ The coating was then dried with hot air at 100°C for 120 seconds.

[0078] ------------------------------------------------------------------ Composition of coating liquid for forming alignment film -------------------------------------------------- Modified polyvinyl alcohol shown below: 28 parts by mass Citrate ester (AS3, manufactured by Sankyo Chemical Co., Ltd.) 1.2 parts by mass Photoinitiator (Irgacure 2959, manufactured by BASF) 0.84 parts by mass Glutaraldehyde 2.8 parts by mass Water 699 parts by mass Methanol 226 parts by mass ------------------------------------------------------------------

[0079] (Modified polyvinyl alcohol)

[0080] The cellulose acylate film having the alignment layer formed thereon was used as a support (transparent substrate). One surface of the support was subjected to rubbing treatment (rayon cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm (revolutions per minute), conveyance speed: 10 m / min, number of strokes: 1 round trip) in a direction rotated 45° clockwise from the long side direction of the support.

[0081] The following retardation layer-forming coating solution was applied to the rubbed surface of the alignment film on the support using a wire bar, and then dried.

[0082] (Coating liquid for forming retardation layer) The following components were mixed to prepare a coating liquid for forming retardation layer having the following composition: Mixture 1: 100 parts by mass Fluorine-based horizontal alignment agent 1 (alignment control agent 1): 0.05 parts by mass Fluorine-based horizontal alignment agent 2 (alignment control agent 2): 0.01 parts by mass Polymerization initiator IRGACURE OXE01 (manufactured by BASF) 1.0 part by mass Solvent (methyl ethyl ketone): amount to give a solute concentration of 20% by mass

[0083]

[0084]

[0085]

[0086] Then, the sample was placed on a hot plate at 50°C and heated with an electrodeless lamp "D bulb" (60 mW / cm) manufactured by Fusion UV Systems in an environment with an oxygen concentration of 1000 ppm or less. 2 ) for 6 seconds to fix the liquid crystal phase. As a result, a retardation layer having a desired front retardation, i.e., a desired retardation, was obtained. The retardation of the prepared retardation layer was measured with an AxoScan and found to be 126 nm.

[0087] The following cholesteric liquid crystal layer forming coating solution B1 was applied to the surface of the obtained retardation layer at room temperature using a wire bar so that the thickness of the dried film after drying would be 0.3 μm, thereby obtaining a coating layer.

[0088] (Coating Solution B1 for Forming Cholesteric Liquid Crystal Layer) The following components were mixed to prepare a coating solution for forming a cholesteric liquid crystal layer having the following composition. The amount of the right-handed chiral agent used was adjusted so that the selective reflection central reflection wavelength was 450 nm. Mixture 1: 100 parts by mass Fluorine-based horizontal alignment agent 1 (Alignment control agent 1): 0.05 parts by mass Fluorine-based horizontal alignment agent 2 (Alignment control agent 2): 0.02 parts by mass Right-handed chiral agent LC756 (manufactured by BASF) Polymerization initiator IRGACURE OXE01 (manufactured by BASF) 1.0 part by mass Solvent (methyl ethyl ketone): amount to give a solute concentration of 20% by mass

[0089] The coated layer was dried at room temperature for 30 seconds and then heated for 2 minutes in an atmosphere at 85° C. Thereafter, in an environment with an oxygen concentration of 1000 ppm or less, the coated layer was irradiated with ultraviolet light at 60% output for 6 to 12 seconds using a D bulb (90 mW / cm lamp) manufactured by Fusion Electronics at 60° C. to fix the cholesteric liquid crystal phase, thereby obtaining a cholesteric liquid crystal layer B1 having a thickness of 0.3 μm.

[0090] Next, the same process was repeated using the cholesteric liquid crystal layer forming coating solution G1 on the surface of the obtained cholesteric liquid crystal layer B1, to laminate a cholesteric liquid crystal layer G1 having a thickness of 0.54 μm. The cholesteric liquid crystal layer forming coating solution G1 had the same composition as the cholesteric liquid crystal layer forming coating solution B1, except that the amount of the right-handed chiral dopant used was changed so that the selective reflection center wavelength was 680 nm.

[0091] Next, the same process was repeated using the cholesteric liquid crystal layer forming coating solution R1 on the surface of the obtained cholesteric liquid crystal layer G1, to laminate a cholesteric liquid crystal layer R1 having a thickness of 0.36 μm. The cholesteric liquid crystal layer forming coating solution R1 had the same composition as the cholesteric liquid crystal layer forming coating solution R1, except that the amount of the right-handed chiral dopant used was changed so that the selective reflection center wavelength was 820 nm.

[0092] In this way, a reflective layer having three cholesteric liquid crystal layers was obtained on the retardation layer. Next, a polarization conversion layer-forming coating liquid was applied to the surface of the obtained cholesteric liquid crystal layer to form a polarization conversion layer, thereby producing a reflective film including a reflective layer. The polarization conversion layer had a thickness of 1.7 μm. The polarization conversion layer was formed in the same manner as in the formation of the cholesteric liquid crystal layer described above. The amount of right-handed chiral agent used in the polarization conversion layer-forming coating liquid was such that when a single cholesteric liquid crystal layer with a thickness of 3 μm was formed using the polarization conversion layer-forming coating liquid, the selective reflection center wavelength of the cholesteric liquid crystal layer was 10,000 nm. The pitch number of the polarization conversion layer was 0.265.

[0093] (Polarization conversion layer forming coating liquid) The following components were mixed to prepare a polarization conversion layer forming coating liquid having the following composition: Mixture 1: 100 parts by mass Fluorine-based horizontal alignment agent 1 (alignment control agent 1): 0.05 parts by mass Fluorine-based horizontal alignment agent 2 (alignment control agent 2): 0.02 parts by mass Right-handed chiral agent LC756 (manufactured by BASF) Polymerization initiator IRGACURE OXE01 (manufactured by BASF): 1.0 part by mass Solvent (methyl ethyl ketone): amount to give a solute concentration of 20% by mass

[0094] <Preparation of Windshield Glass> A first glass plate (FL2, manufactured by Central Glass Co., Ltd., visible light transmittance 90%) measuring 200 mm in length, 300 mm in width, and 2 mm in thickness was prepared as the first and second glass plates. A 0.76 mm-thick PVB film manufactured by Sekisui Chemical Co., Ltd. was prepared as the interlayer. The heat seal layer was formed as follows. First, the following components were mixed to prepare a coating solution for forming a heat seal layer: PVB sheet piece (S-LEC film, manufactured by Sekisui Chemical Co., Ltd.) 5.0 parts by mass; Methanol 90.25 parts by mass; Butanol 4.75 parts by mass. Next, the coating solution for forming a heat seal layer was applied to an optical film using a wire bar, dried, and heat-treated at 50°C for 1 minute to obtain a heat seal layer with a thickness of 1 μm. The optical film used above was 100 mm in length and 100 mm in width.

[0095] Next, a first glass plate, an optical film with a heat-sealing layer, an interlayer film, and a second glass plate were laminated in this order, and the resulting laminate was held at 90°C and 10 kPa (0.1 atm) for one hour, and then heated in an autoclave (manufactured by Kurihara Seisakusho) at 115°C and 1.3 MPa (13 atm) for 20 minutes to remove air bubbles, thereby obtaining a windshield glass. The heat-sealing layer was positioned toward the first glass plate. The optical film was positioned near the center of the first glass plate.

[0096] A reflective film was attached to the surface of the second glass plate of the windshield glass obtained above opposite the interlayer film side using an adhesive layer (OCA) (15 μm, manufactured by Lintec), to produce the windshield glass used in Example 1. The reflective film was attached so that the polarization conversion layer in the reflective film faced the second glass plate side.

[0097] Windshield glasses were produced according to the same procedure as in Example 1, except that the composition ratio of materials used in producing the optical film, the thickness of the optical film, the irradiation angle of light during exposure, and the width of the opening in the mask were adjusted so as to achieve the "tilt angle," "haze," "refractive index difference," "thickness," "width," and "Δnd" shown in Table 1 below, and the configuration of each component was set as shown in Table 1. The "Configuration" column in Table 1 describes the configuration of the windshield glasses used in each Example. In Examples 1 to 4 and Comparative Examples 2 and 3, the windshield glasses had a first glass plate / optical film / interlayer film / second glass plate / OCA / polarization conversion layer / cholesteric liquid crystal layer / retardation layer, in this order. In Example 5, the windshield glass had a first glass plate / optical film / interlayer film / second glass plate, in this order. In Comparative Example 1, the windshield glass had a first glass plate / interlayer film / second glass plate / OCA / polarization conversion layer / cholesteric liquid crystal layer / retardation layer, in this order. The "Tilt Angle" column in Table 1 indicates the angle between the normal to the optical film surface and the direction in which the high refractive index region and the low refractive index region extend. In all Examples and Comparative Examples, the angle between the normal to the optical film surface and the direction in which the high refractive index region extends, and the angle between the normal to the optical film surface and the direction in which the low refractive index region extends, are the same, and these values ​​are shown in Table 1. The "Haze" column in Table 1 indicates the haze measured from the normal to the optical film. The "Refractive Index Difference" column in Table 1 indicates the difference between the refractive index of the high refractive index region and the refractive index of the low refractive index region in the optical film. The "Thickness" column in Table 1 indicates the thickness of the optical film. The "Width" column in Table 1 indicates the width of the high refractive index region (width WH in FIG. 4 ) and the width of the low refractive index region (width WL in FIG. 4 ) on the surface of the optical film (the surface opposite the PET substrate side). In all Examples and Comparative Examples, the width of the high refractive index region and the width of the low refractive index region are the same, and these values ​​are shown in Table 1. The "Δnd" column in Table 1 represents the product Δnd of the difference Δn between the refractive index of the high refractive index region and the refractive index of the low refractive index region and the thickness d.

[0098] <Evaluation of Double Images> An image of diagonal grid white lines on a black background displayed on an iPad (registered trademark) was projected onto the windshield glass of each example and comparative example at an incident angle of 70°, and the secondary image (double image) seen on top of the main image was observed and evaluated according to the following criteria. The positional relationship between the iPad (registered trademark) and the windshield glass corresponds to the aspect in which the iPad (registered trademark) is placed in the position of the projector shown in Figure 2. A: No double image is visible. B: The double image is very faint (at a level that does not cause any problems in actual use). C: The double image is clearly visible.

[0099] <Evaluation of visibility> With the windshield glass positioned as described above for <Evaluation of double images>, an LED light was shone on the observer from the outside, across the windshield glass, from the observer's position, and the ease of visibility of the outside world was evaluated according to the following criteria: A: The glass was almost cloudy and the outside world was clearly visible. B: The glass was cloudy and the outside world was difficult to see.

[0100] <Evaluation of rainbow unevenness> An image of white letters on a black background displayed on an iPad (registered trademark) was irradiated at an incident angle of 70° onto the windshield glass placed in the position described above for <Evaluation of double images>, and the main image was observed and evaluated according to the following criteria: A: Only the colored letters were visible. B: Faint blue, green, and red letters were visible at a distance from the main image.

[0101]

[0102] As shown in Table 1, it was confirmed that the desired effects were obtained when the optical film of the present invention was used. In particular, from a comparison of Examples 1 and 5 with the other Examples, it was confirmed that better effects were obtained when Δnd was in the range of 0.20 to 0.30 μm.

[0103] 10, 100 Head-up display system 12, 102 Windshield glass 14, 104 Projector 20 First glass plate 22 Optical film 24 Interlayer 26 Second glass plate 28 Reflective layer 30 High refractive index region 32 Low refractive index region 40 Precursor layer 42 Mask

Claims

1. An optical film having high refractive index regions and low refractive index regions alternately along one direction within the plane of the optical film, in a cross section cut in the thickness direction along the one direction, the high refractive index regions and the low refractive index regions all extend in a direction inclined with respect to the normal direction of the surface of the optical film, and the angle between the normal direction and the extension direction of the high refractive index regions and the angle between the normal direction and the extension direction of the low refractive index regions are both 36 to 50 degrees, and the haze measured from the normal direction of the optical film is 2.0% or less.

2. The optical film according to claim 1, wherein the thickness d of the optical film is 1 to 50 μm.

3. The optical film according to claim 1, wherein the difference Δn between the refractive index of the high refractive index region and the refractive index of the low refractive index region is 0.005 to 0.

5.

4. The optical film according to claim 1, wherein the product of the thickness d of the optical film and the difference Δn between the refractive index of the high refractive index region and the refractive index of the low refractive index region is 0.20 to 0.30 μm.

5. The optical film according to claim 1, wherein in the one direction, the width of the high refractive index region at the surface of the optical film and the width of the low refractive index region at the surface of the optical film are both 1.0 to 3.0 μm.

6. A windshield glass comprising a first glass plate, the optical film according to any one of claims 1 to 5, an interlayer film, and a second glass plate.

7. The windshield glass according to claim 6, further comprising a reflective layer on the side of said second glass sheet opposite said interlayer film side.

8. A head-up display system comprising the windshield glass according to claim 6 and a projector that projects projection light onto the windshield glass.

9. The head-up display system according to claim 8, wherein the projection light is P-polarized light, and the angle of incidence of the projection light on a windshield glass is 60 to 75 degrees.

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