Optical laminate for head-up display, functional glass, and head-up display system

Abstract

The present invention pertains to an optical laminate (10) for a head-up display, the optical laminate (10) comprising (A) at least one polyvinyl acetal resin layer (101) having a photoelasticity coefficient (PeA) in the range indicated by formula (1) below, and (B) at least one optically functional layer (102). The present invention also pertains to head-up display functional glass (20) comprising the optical laminate (10), and to a head-up display provided with the optical laminate (10) or the functional glass (20). (1): |PeA| ≤ 4.0×10-11 Pa-1

Description

[Technical Field]

[0001] The present invention relates to an optical laminate suitable for use in, for example, a head-up display, a functional glass, and a head-up display using the same. [Background technology]

[0002] Navigation systems, head-up displays (hereinafter also referred to as "HUDs"), etc. are used as methods for displaying information to drivers of automobiles, aircraft, etc. HUDs are systems that project images from image display means such as liquid crystal displays (hereinafter also referred to as "LCDs") onto, for example, the windshield of an automobile.

[0003] The light emitted from the image display means is reflected by a reflector and then by the windshield before reaching the viewer. The viewer sees the image projected onto the windshield, but the image appears to be located further away than the windshield. This method allows the driver to obtain various information while gazing fixedly at the road ahead through the windshield, with almost no movement of the eyes, making it safer than conventional car navigation systems that require the driver to shift their gaze.

[0004] In HUD systems, the displayed information is projected and superimposed on the view actually seen through the windshield, but because the displayed light is reflected by two surfaces, one on the inside and one on the outside of the windshield, the reflected image appears as a double image, making the displayed information difficult to see.

[0005] It is known that the problem of reflected double images can be solved by using a phase difference element that can change the polarization direction by 90° on an automobile windshield. For example, Patent Document 1 discloses that when S-polarized display light is incident at the Brewster angle on an automobile windshield equipped with a film-like polarization rotator inside, part of the S-polarized light is reflected by the surface of the windshield on the inside of the vehicle, the S-polarized light that passes through the surface is converted to P-polarized light by the polarization rotator, and then all of the P-polarized light is emitted outside the vehicle on the surface of the windshield on the outside of the vehicle, thereby preventing double images.

[0006] Another known technique for suppressing double images is to use a light control film in which a circularly polarized reflective film made using a cholesteric liquid crystal layer is sandwiched between two quarter-wave plates and P-polarized light is incident (Patent Document 2). In this technique, incident linearly polarized light is converted into circularly polarized light by the quarter-wave plate, and the circularly polarized light is reflected by the light reflective film made using a cholesteric liquid crystal layer, making it visible to the observer.

[0007] As described above, optical laminates used in head-up displays are generally manufactured by stacking multiple films with various functions, but uneven performance is likely to occur within the surface of the laminate, making it difficult to achieve uniform performance within the surface. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-40271 [Patent Document 2] Patent No. 5973109 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide an optical laminate for a head-up display, which has excellent in-plane performance uniformity, a functional glass, and a head-up display system using the same. [Means for solving the problem]

[0010] An optical laminate for a head-up display according to an embodiment of the present invention comprises (A) at least one polyvinyl acetal resin layer having a photoelastic coefficient (PeA) within the range of the following formula (1), and (B) at least one optically functional layer:

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[0011] In one embodiment of the present invention, the optical laminate for a head-up display further comprises (C) at least one polyvinyl acetal resin layer having a photoelastic coefficient (PeC) within the range of the following formula (2):

number

[0012] In one embodiment of the present invention, the optical laminate for a head-up display has two polyvinyl acetal resin layers having different photoelastic coefficients (Pe), and a ratio (PeR) of a photoelastic coefficient (Pe2) of one of the polyvinyl acetal resin layers to a photoelastic coefficient (Pe1) of the other polyvinyl acetal resin layer satisfies the following formula (3), <Pe2である。

number

[0013] In one embodiment of the present invention, the polyvinyl acetal resin layer has a thickness of 10 μm or more and 800 μm or less.

[0014] In one embodiment of the present invention, the polyvinyl acetal resin layer is a polyvinyl butyral resin layer.

[0015] In one embodiment of the present invention, the optical functional layer is (B-1) a half-wave plate or (B-5) a film having a P-polarized light reflecting function.

[0016] In one embodiment of the present invention, the optical functional layer is (B-1) a half-wave plate, (B-2) a quarter-wave plate, (B-3) a laminate of a half-wave plate and a circularly polarized light reflective layer, or (B-4) a laminate of a quarter-wave plate and a circularly polarized light reflective layer.

[0017] In one embodiment of the present invention, the half-wave plate or the quarter-wave plate includes a polymerizable liquid crystal layer as a layer having a function of converting a polarization axis.

[0018] A functional glass for a head-up display according to an embodiment of the present invention comprises the optical laminate and (D) a glass plate.

[0019] A head-up display system according to an embodiment of the present invention includes the optical laminate or the functional glass.

[0020] In one embodiment of the present invention, the head-up display system includes the functional glass, and the incident angle at which light emitted from the display image projection means enters the functional glass is in the range of α-10° to α+10° with respect to Brewster's angle α. [Effects of the Invention]

[0021] According to the present invention, it is possible to realize an optical laminate, functional glass, and a head-up display system using the same, which have excellent in-plane performance uniformity and are suitable for application to head-up displays. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a side cross-sectional view showing one embodiment of an optical laminate according to the present invention. [Figure 2]FIG. 2 is a side cross-sectional view showing another embodiment of the optical laminate according to the present invention. [Figure 3] FIG. 3 is a side cross-sectional view showing one embodiment of the functional glass according to the present invention. [Figure 4] FIG. 4 is a schematic diagram showing an embodiment of a head-up display system according to the present invention. [Figure 5] FIG. 5 is a schematic diagram showing an outline of how light emitted from a display image projection means is incident on the functional glass according to the present invention at a near Brewster angle of incidence. [Figure 6] FIG. 6 is a schematic diagram showing another embodiment of a head-up display system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments according to the present invention will be described with reference to the drawings. Note that the following embodiments merely exemplify some typical embodiments of the present invention, and various modifications can be made within the scope of the present invention. In addition, hereinafter, the expression "for head-up displays" may be omitted, and the description may simply refer to optical laminates and functional glass. Furthermore, terms such as "(meth)acryloyl" and "(meth)acrylate" mean "acryloyl" or "methacryloyl," "acrylate" or "methacrylate," respectively. Furthermore, "head-up displays" may also be expressed as HUDs.

[0024] <Optical laminate> FIG. 1 shows one embodiment of an optical laminate according to the present invention. As shown in FIG. 1, the optical laminate 10 includes a polyvinyl acetal resin layer 101 having a photoelastic coefficient within a predetermined range and an optical functional layer 102. Such an optical laminate 10 has small in-plane variations in polarized light transmittance. Therefore, when the optical laminate 10 is applied to the windshield of a head-up display system, for example, the occurrence of double images due to the projection position can be suppressed. In other words, the optical laminate 10 according to this embodiment has little dependency on the projection position, and therefore has excellent performance uniformity within the plane of the optical laminate 10. Therefore, when the optical laminate 10 according to this embodiment is applied to a head-up display system, the occurrence of double images can be suppressed over a wide area regardless of the projection position, allowing the viewer to use the head-up display system without stress.

[0025] [Polyvinyl acetal resin layer] The optical laminate according to the present invention comprises, as component (A), at least one polyvinyl acetal resin layer having an optical elastic coefficient (PeA) within the range of the following formula (1). When the optical laminate according to this embodiment is used in functional glass described below, the polyvinyl acetal resin layer functions as an interlayer film for laminated glass. Furthermore, when the optical laminate includes multiple polyvinyl acetal resin layers having different optical elastic coefficients (PeA), the materials of the polyvinyl acetal resin layers may be the same or different, but are preferably the same.

[0026]

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[0027] <Composition of the polyvinyl acetal resin layer> The polyvinyl acetal resin layer contains at least one polyvinyl acetal resin, which is a resin obtained by reacting polyvinyl alcohol with an aldehyde, such as a compound represented by the following formula (I):

[0028] [ka]

[0029] In formula (I), R represents a C1 to C10 linear, branched, or cyclic alkyl group, preferably a C1 to C6 linear alkyl group, more preferably a C1 to C4 linear alkyl group, particularly preferably C1, i.e., a methyl group (polyvinyl acetoacetal resin), or C4, i.e., an n-butyl group (polyvinyl butyral resin), and most preferably an n-butyl group. When R is an n-butyl group, there is little change in hue, particularly before and after a durability test, and it is highly practical.

[0030] In the above formula (I), n represents the number of repeating units and is preferably 50 or more and 1500 or less. The upper limit of n is preferably 1000, more preferably 800, particularly preferably 600, and most preferably 200. The lower limit is preferably 70, more preferably 100, particularly preferably 120, and most preferably 150. That is, n is most preferably 150 or more and 200 or less.

[0031] The weight-average molecular weight of the polyvinyl acetal resin is preferably 6,000 or more and 1,000,000 or less. The upper limit is preferably 120,000, more preferably 96,000, particularly preferably 60,000, and most preferably 20,000. The lower limit is preferably 8,500, more preferably 10,000, particularly preferably 12,000, and most preferably 16,000. That is, the most preferable weight-average molecular weight is 16,000 or more and 20,000 or less. The weight-average molecular weight is a value measured by gel permeation chromatography (GPC).

[0032] The polyvinyl acetal resin layer is preferably a transparent polyvinyl acetal resin layer formed from a resin composition containing a polyvinyl acetal resin having a vinyl acetate component (residual acetyl groups) of 14 mol% or less, which is obtained by acetalizing polyvinyl alcohol with an aldehyde having 3 to 4 carbon atoms, and a plasticizer. The resin composition for forming the polyvinyl acetal resin layer may further contain inorganic fine particles, heat-shielding fine particles, a light-shielding agent, various dyes and / or pigments, etc., as necessary.

[0033] The plasticizer is not particularly limited, but known plasticizers commonly used for this type of interlayer film can be used. For example, triethylene glycol-di-2-ethylbutyrate (3GH), triethylene glycol-di-2-ethylhexanoate (3GO), triethylene glycol-di-n-heptanoate (3G7), tetraethylene glycol-di-2-ethylhexanoate (4GO), tetraethylene glycol-di-n-heptanoate (4G7), and oligoethylene glycol-di-2-ethylhexanoate (NGO) are preferably used. These plasticizers are generally used in an amount of 25 to 70 parts by mass per 100 parts by mass of the polyvinyl acetal resin.

[0034] Examples of inorganic fine particles include calcium carbonate, alumina, kaolin clay, calcium silicate, magnesium oxide, magnesium hydroxide, aluminum hydroxide, magnesium carbonate, talc, feldspar powder, mica, baryte, barium carbonate, titanium oxide, silica, and glass beads. These may be used alone or in combination. The average particle size of the inorganic fine particles is preferably 1 nm to 150 nm, more preferably 5 nm to 120 nm, and particularly preferably 10 nm to 100 nm. The average particle size can be measured by dynamic light scattering using a light scattering measurement device (e.g., Otsuka Electronics' "DLS-6000AL") with an Ar laser as a light source. The inorganic fine particles are generally used in an amount of 1 part by mass to 200 parts by mass, preferably 5 parts by mass to 150 parts by mass, and more preferably 10 parts by mass to 100 parts by mass, per 100 parts by mass of the polyvinyl acetal resin.

[0035] Examples of heat ray shielding fine particles include tin-doped indium oxide (ITO), antimony-doped tin oxide (ATO), aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), tin-doped zinc oxide, silicon-doped zinc oxide, zinc antimonate, lanthanum hexaboride, cerium hexaboride, gold fine powder, silver fine powder, platinum fine powder, and aluminum fine powder.

[0036] Examples of light-shielding agents include carbon black and red iron oxide. Examples of pigments include black pigment carbon black, red pigment (CI Pigment Red), blue pigment (CI Pigment Blue), yellow pigment (CI Pigment Yellow), and a dark reddish-brown mixed pigment obtained by mixing four of these. The amounts of heat-shielding fine particles and light-shielding agent added and their contents are appropriately adjusted to an extent that does not impair the transparency of the polyvinyl acetal resin layer.

[0037] The polyvinyl acetal resin layer used in the present invention may further contain various additives such as ultraviolet absorbers, antioxidants, and adhesion modifiers that are used in this type of interlayer film.

[0038] Preferred examples of ultraviolet absorbers include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, and 2-(2'-hydroxy-3',5'-di-amylphenyl)benzotriazole. Hindered amine light stabilizers are also preferred.

[0039] Preferred antioxidants include t-butylhydroxytoluene, tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, etc. Preferred adhesion modifiers are alkali metal salts or alkaline earth metal salts of organic or inorganic acids.

[0040] <About the photoelastic coefficient (Pe)> The photoelastic coefficient is a proportional coefficient of birefringence or retardation that occurs in proportion to stress, and has a constant value for each composition of the polyvinyl acetal resin layer. The unit of the photoelastic coefficient is Pa. -1 In the optical laminate according to this embodiment, at least one polyvinyl acetal resin layer has a photoelastic coefficient (PeA) within the range of the above formula (1). When the photoelastic coefficient (PeA) of the polyvinyl acetal resin layer as component (A) satisfies this condition, the unevenness of the polarized light transmittance within the plane of the optical laminate is reduced, and double images can be effectively prevented. Note that, although it is preferable that the polarized light transmittance is uniform within the plane, it is particularly preferable that the polarized light transmittance is low and uniform within the plane.

[0041] The above formula (1) is based on the absolute value of the photoelastic coefficient (PeA) of 4.0 × 10 -11 (Pa -1 ) or less, that is, the photoelastic coefficient (PeA) is -4.0 × 10 -11 (Pa -1 ) or more than 4.0 × 10 -11 (Pa -1The lower limit of the photoelastic coefficient (PeA) is -4.0×10 -11 (Pa -1 ), but more preferable values ​​are -3.0×10 -11 (Pa -1 ), -2.0×10 -11 (Pa -1 ), -1.0×10 -11 (Pa -1 ), -9.0×10 -12 , -6.0×10 -12 (Pa -1 ), -5.0×10 -12 (Pa -1 ), -2.0×10 -12 (Pa -1 ), -1.0×10 -12 (Pa -1 ), 0, 1.0×10 -14 (Pa -1 ), 5.0×10 -14 (Pa -1 ), 1.0×10 -13 and particularly preferably 5.0 × 10 -13 (Pa -1 ) The upper limit of the photoelastic coefficient (PeA) is 4.0 × 10 -11 (Pa -1 ), but more preferable values ​​are 3.0×10 -11 (Pa -1 ), 2.0×10 -11 (Pa -1 ), 1.0×10 -11 (Pa -1 ), 9.0×10 -12 , 6.0×10 -12 (Pa -1 ), 5.0×10 -12 (Pa -1 ), 2.0×10 -12 (Pa -1 ), and particularly preferably 1.0 × 10 -12 (Pa -1 Therefore, the most preferable range of the photoelastic coefficient (PeA) is 5.0 × 10 -13 (Pa -1 ) or more than 1.0 × 10 -12 (Pa -1 ) is as follows.

[0042] In the optical laminate according to this embodiment, the polyvinyl acetal resin layer preferably further comprises, as structure (C), at least one polyvinyl acetal resin layer having a photoelastic coefficient (PeC) within the range of the following formula (2). The polyvinyl acetal resin layer in structure (C) may be made of the same material as or a different material from the polyvinyl acetal resin layer in structure (A), but is preferably made of the same material. Furthermore, when the optical laminate includes multiple polyvinyl acetal resin layers having different photoelastic coefficients (PeC), the materials of the polyvinyl acetal resin layers may be the same or different.

[0043]

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[0044] The lower limit of the photoelastic coefficient (PeC) is 5.0 x 10 -11 (Pa -1 ), but more preferable values ​​are 6.0×10 -11 (Pa -1 ), 7.0×10 -11 (Pa -1 ), 8.0×10 -11 (Pa -1 ), 9.0×10 -11 , 1.0×10 -10 (Pa -1 ), and particularly preferably 1.5 × 10 -10 (Pa -1 ) The upper limit of the photoelastic coefficient (PeC) is 5.0 × 10 -9 (Pa -1 ), but more preferable values ​​are 4.0×10 -9 (Pa -1 ), 3.0×10 -9 (Pa -1 ), 2.0×10 -9 (Pa -1 ), 1.0×10 -9 , 8.0×10 -10 (Pa -1 ), and particularly preferably 5.0 × 10 -10 (Pa -1Therefore, the most preferable range of the photoelastic coefficient (PeC) is 1.5 × 10 -10 (Pa -1 ) or more than 5.0 × 10 -10 (Pa -1 ) is as follows.

[0045] FIG. 2 shows another embodiment of the optical laminate of the present invention, in which an optically functional layer 102 is sandwiched between two polyvinyl acetal resin layers 101. In such an embodiment, the optical laminate 10 may have one polyvinyl acetal resin layer as a polyvinyl acetal resin layer having structure (A), and the other polyvinyl acetal resin layer as a polyvinyl acetal resin layer having structure (C). Furthermore, when the optical laminate 10 has two polyvinyl acetal resin layers having different photoelastic coefficients (Pe), it is preferable that the ratio (PeR) of the photoelastic coefficient (Pe1) of one polyvinyl acetal resin layer to the photoelastic coefficient (Pe2) of the other polyvinyl acetal resin layer satisfies the following formula (3). However, in formula (3), Pe1 <Pe2である。

[0046]

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[0047] In this way, by having the photoelastic coefficients of the two polyvinyl acetal resin layers differ from each other within a range that satisfies formula (3), unevenness in the polarized light transmittance in the plane of the optical laminate is reduced, and double images can be effectively prevented. For example, one of the two polyvinyl acetal resin layers may be a polyvinyl acetal resin layer having structure (A) and the other a polyvinyl acetal resin layer having structure (C), so that the photoelastic coefficients satisfy formula (3). In formula (3), the lower limit of the ratio of photoelastic coefficients (PeR) is 10, more preferably 20, 30, 50, 70, 80, 100, 200, and 250, in that order, and particularly preferably 280. Furthermore, the upper limit of the ratio of photoelastic coefficients (PeR) is 1000, more preferably 900, 800, 700, 600, 500, 450, and 400, in that order, and particularly preferably 350. Therefore, the most preferable range of the photoelastic coefficient ratio (PeR) is 280 or more and 350 or less.

[0048] <Thickness of the polyvinyl acetal resin layer> The thickness of the polyvinyl acetal resin layer is preferably 10 μm or more and 1200 μm or less, and more preferably 10 μm or more and 800 μm or less. When the thickness of the polyvinyl acetal resin is in this range, when the optical laminate according to this embodiment is used in functional glass, the functional glass can be imparted with good impact resistance and penetration resistance. Furthermore, when the optical laminate has two or more polyvinyl acetal resin layers, the thicknesses of the polyvinyl acetal resin layers may be the same or different.

[0049] <Manufacturing method> The polyvinyl acetal resin used in the present invention can be produced using known methods. For example, a specific polyvinyl alcohol is dissolved in warm water, and the resulting aqueous solution is maintained at a specific temperature, for example, 0 to 95°C, and a required acid catalyst and a specific aldehyde are added. Next, the acetalization reaction is allowed to proceed with stirring, and the reaction temperature is further increased to complete the reaction. Thereafter, neutralization, water washing, and drying are carried out to produce a powder of the polyvinyl acetal resin.

[0050] (placement) The polyvinyl acetal resin layer is preferably disposed as the outermost layer of the optical laminate according to this embodiment. The outermost layer refers to the layer that comes into contact with the glass plate when the optical laminate according to this embodiment is disposed on a functional glass having a (D) glass plate, which will be described later. By disposing the polyvinyl acetal resin layer as the outermost layer of the optical laminate, the impact resistance and penetration resistance of the functional glass are improved, and furthermore, shattering of the glass can be prevented.

[0051] (Method for forming polyvinyl acetal resin layer) The polyvinyl acetal resin layer can be produced by kneading a resin composition containing a polyvinyl acetal resin, a plasticizer, and various additives added as needed using an extruder, plastograph, kneader, Banbury mixer, calendar roll, etc., and then forming the kneaded mixture into a sheet using a conventional film-forming method such as extrusion, calendaring, or pressing. The polyvinyl acetal resin layer may be formed by coating and drying a solution of the polyvinyl acetal resin, a plasticizer, and various additives added as needed in a solvent such as methyl ethyl ketone on a desired substrate, or by directly forming a film on one or both sides of the (B) optical functional layer described below.

[0052] [Optical functional layer] The optical laminate according to this embodiment includes at least one optically functional layer as component (B). The optically functional layer used in the present invention is not particularly limited as long as it has the function of converting the polarization axis of incident light, and can be appropriately designed to obtain the desired polarization. Examples include retardation films such as half-wave plates and quarter-wave plates, laminates of multiple retardation films, and laminates of these films with a circularly polarized light reflective layer. Specific examples include (B-1) a half-wave plate, (B-2) a quarter-wave plate, (B-3) a laminate of a half-wave plate and a circularly polarized light reflective layer, and (B-4) a laminate of a quarter-wave plate and a circularly polarized light reflective layer. The circularly polarized light reflective layer is preferably, for example, a cholesteric liquid crystal layer using a cholesteric liquid crystal.

[0053] When the optical laminate according to this embodiment is applied to a HUD, it is particularly preferable to use a (B-1) half-wave plate or a (B-5) film having a P-polarized light reflection function, i.e., a film that selectively reflects P-polarized light, as the optical functional layer. Examples of light-reflecting layers that reflect P-polarized light include birefringence interference polarizers made of a polymer multilayer film made of two or more polymers with different refractive indices, polarizers having a fine uneven structure called wire grid polarizers, and laminates of a quarter-wave plate and a circularly polarized light reflective layer, such as an optical laminate film in which a circularly polarized light reflective film made of a cholesteric liquid crystal layer is sandwiched between two quarter-wave plates. In such optical laminate films, incident P-polarized light is converted into circularly polarized light by the quarter-wave plate, and then the circularly polarized light is reflected by the cholesteric liquid crystal layer and converted back into P-polarized light by the quarter-wave plate. That is, the optical functional layer is preferably (B-1) one or more half-wave plates, or (B-4) a laminate in which one or more circularly polarized light reflective layers are sandwiched between two quarter-wave plates.

[0054] <1 / 2 wavelength version> When a half-wave plate is used as the optical functional layer, the half-wave plate is a retardation element that converts P-polarized light to S-polarized light or S-polarized light to P-polarized light, i.e., converts the polarization axis. Such a half-wave plate can be obtained, for example, by uniaxially stretching a film made of polycarbonate or cycloolefin polymer so that the retardation is half the wavelength, or by orienting a horizontally oriented polymerizable liquid crystal to a thickness that results in a retardation of half the wavelength. Generally, a half-wave plate using a horizontally oriented polymerizable liquid crystal is composed of a polymerizable liquid crystal layer that converts the polarization axis and a support substrate on which a coating liquid forming the polymerizable liquid crystal layer is applied. However, the support substrate is not an essential component of the optical functional layer; the polymerizable liquid crystal layer can also be transferred to other substrates (e.g., a polyvinyl acetal resin layer or a glass plate) for use.

[0055] The upper limit of the thickness of such a half-wave plate is preferably 10 μm or less, more preferably 5 μm or less, from the viewpoint of the alignment of the liquid crystal. On the other hand, the lower limit of the thickness of the half-wave plate is preferably 0.3 μm or more, more preferably 0.5 μm or more, from the viewpoint of the polymerizability of the liquid crystal. When light is incident obliquely onto the main surface of the half-wave plate, the phase difference may change depending on the angle of incidence of the light. In such a case, in order to more precisely adapt the phase difference, for example, a phase difference element whose refractive index is adjusted can be used to suppress the change in phase difference due to the angle of incidence. For example, when the refractive index in the slow axis direction in the plane of the phase difference element is nx, the refractive index in the direction perpendicular to nx in the plane of the phase difference element is ny, and the refractive index in the thickness direction of the phase difference element is nz, the coefficient Nz expressed by the following formula (4) is preferably controlled to be 0.3 to 1.0, more preferably 0.5 to 0.8.

[0056]

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[0057] When an optical laminate having a half-wave plate as an optical functional layer is provided in the functional glass of the present invention described below and the functional glass is applied to a HUD system, in order to efficiently convert P-polarized light to S-polarized light or S-polarized light to P-polarized light in the HUD system, it is preferable to control the angle θ between the polarization axis of S-polarized light or P-polarized light incident from a position tilted at an angle of 45° to 65° from the axis perpendicular to the surface of the functional glass and the slow axis of the half-wave plate to 35° to 47°. By setting the angle of incidence of S-polarized light or P-polarized light incident on the half-wave plate to a range of 45° to 65°, when P-polarized light enters the functional glass, the reflectance at the surface of the functional glass can theoretically be reduced to 2% or less. The transmitted P-polarized light is converted to S-polarized light by the half-wave plate, and the converted S-polarized light is reflected at the interface between the incident side and the air of the functional glass on the opposite side. The reflected S-polarized light is converted back to P-polarized light by the half-wave plate, and this P-polarized light reaches the viewer. Furthermore, when S-polarized light enters functional glass, it is reflected from the surface of the glass and reaches the viewer. The transmitted S-polarized light is converted to P-polarized light by the half-wave plate, and the converted P-polarized light passes through without being reflected by the functional glass on the opposite side or the interface between the functional glass and air. Thus, controlling the incident angle of S-polarized or P-polarized light entering the functional glass can reduce the occurrence of double images. Furthermore, if the angle θ is less than 35° or greater than 47°, the polarization axis conversion performance of the functional glass, which converts P-polarized light to S-polarized light or S-polarized light to P-polarized light, may be impaired, resulting in a darker image displayed on the display. By appropriately controlling this angle θ, the half-wave plate exhibits good polarization axis conversion performance, resulting in a clearer image.

[0058] In order to appropriately control the polarization axis conversion performance exhibited by the half-wave plate, it is preferable that the angle θ is a value calculated from the following formulas (5) and (6). Here, the technical significance of the following formulas (5) and (6) will be explained. When S-polarized or P-polarized light incident on the functional glass passes through the half-wave plate, which is a medium having a refractive index different from that of air, the angle of incidence at which it is incident on the half-wave plate changes. Here, the angle of incidence of S-polarized or P-polarized light on the functional glass is α, the angle of incidence at which it actually enters the half-wave plate, i.e., the refraction angle of the half-wave plate, is β, and the refractive index of air is n. α , the refractive index of the half-wave plate is n β Then, according to Snell's law, sinα / sinβ=n β / n αholds, and simplifying this equation to obtain β yields equation (6). Meanwhile, if the polarization axis of S-polarized light incident on the functional glass is the x-axis, the polarization axis of P-polarized light is the y-axis, and the angle between the y-axis and the slow axis of the half-wave plate is θ, and the retardation value is Re, vector analysis can express the y-axis as Re·cosθ and the x-axis as Re·sinθ. Here, it is known that the polarization axis conversion performance of a half-wave plate is maximized when light is incident at an angle of 45° relative to the slow axis of the half-wave plate. Therefore, theoretically, the angle of incidence relative to the slow axis of the half-wave plate should be 45°. However, as mentioned above, even if the angle of incidence of S-polarized or P-polarized light incident on the functional glass is θ, in reality, the angle of incidence on the half-wave plate is β. Therefore, when the y-axis (theoretical y-axis) of Re·cosθ is tilted at an angle β around the x-axis, the y-axis (effective y-axis) is calculated as Re·cosθ / effective y-axis = sin(90°-β), and the effective y-axis is expressed as Re·cosθcosβ. As mentioned above, the angle of incidence with respect to the slow axis of the half-wave plate is preferably 45°. To make the angle between the polarization axis of S-polarized or P-polarized light incident on the functional glass and the slow axis of the half-wave plate 45°, the x-axis (Re·sinθ) and the effective y-axis (Re·cosθcosβ) must be equal. Therefore, Re·sinθ = Re·cosθcosβ is found, and by simplifying this equation, we derive equation (5). In this way, by strictly controlling the angle θ in relation to the angle β at which light actually enters the half-wave polarizer based on the values ​​calculated from the following equations (5) and (6), it is possible to make the most of the polarization axis conversion performance of the half-wave plate.

[0059]

number

[0060] The range of the angle θ is preferably controlled to within ±5° of the value of the angle θ, and more preferably within ±3°. If the angle θ is outside the ±5° range of an angle that satisfies the value calculated from the following equations (5) and (6), the efficiency of the polarization axis conversion from P polarization to S polarization exhibited by the half-wave plate may decrease. By controlling the range of the angle θ based on the value calculated from the following equations (5) and (6), it is possible to suppress a decrease in the efficiency of the polarization axis conversion from P polarization to S polarization exhibited by the half-wave plate.

[0061] The refractive index of the half-wave plate substituted into equation (6) is the average refractive index, where nx is the refractive index in the slow axis direction of the half-wave plate, ny is the refractive index in the plane of the half-wave plate perpendicular to nx, and nz is the refractive index in the thickness direction of the half-wave plate. When using a commercially available half-wave plate, the average refractive index can be the value listed in a catalog or similar document. When using a polymerizable liquid crystal (described later) as the material for the half-wave plate, the average refractive index can be expressed as (nx + ny + nz) / 3 = (no + ne) / 2, using the liquid crystal's inherent ordinary and extraordinary refractive indices no and ne. To give a specific example of θ calculated from equations (5) and (6), for example, when the refractive index of air is 1.00, a half-wave plate with a refractive index of 1.55 is used, and the incident angle of S-polarized or P-polarized light is 45°, the value of θ is 42° based on equations (5) and (6), so the range of θ is preferably 37° to 47°, and more preferably 39° to 45°. When the incident angle of S-polarized or P-polarized light is 50°, the value of θ is 41° based on equations (5) and (6), so the range of θ is preferably 36° to 46°, and more preferably 38° to 44°. Furthermore, when the incident angle of S-polarized or P-polarized light is 56°, the value of θ is 40° based on equations (5) and (6), so the range of θ is preferably 35° to 45°, and more preferably 37° to 43°. Furthermore, when the angle of incidence of S-polarized or P-polarized light is 65°, the value of θ is 39° based on equations (5) and (6), so the range of θ is preferably 34° or more and 44° or less, and more preferably 36° or more and 42° or less. By controlling the angle between the polarization axis of S-polarized or P-polarized light incident from a position tilted at an angle of 45° or more and 65° or less from the axis perpendicular to the surface of the functional glass and the slow axis of the half-wave plate to 35° or more and 47° or less, the half-wave plate exhibits good polarization axis conversion performance, and as a result, a HUD system can be provided in which the displayed image is more clearly visible.

[0062] As described above, in the present invention, the polarization axis conversion performance of the half-wave plate can be further improved by controlling the angle θ between the polarization axis of P-polarized or S-polarized light incident on the functional glass and the slow axis of the half-wave plate. In such cases, from the viewpoints of controllability of the slow axis of the half-wave plate and production costs, it is particularly preferable to use a half-wave plate including a polymerizable liquid crystal layer as a layer that converts the polarization axis.

[0063] Polymerizable liquid crystals are nematic liquid crystal monomers that have a polymerizable group in the molecule and exhibit liquid crystallinity within a specific temperature or concentration range. Examples of polymerizable groups include (meth)acryloyl, vinyl, chalconyl, cinnamoyl, and epoxy groups. Furthermore, for polymerizable liquid crystals to exhibit liquid crystallinity, it is preferable for the polymerizable liquid crystal to have a mesogenic group in the molecule. Mesogenic groups refer to rod- or plate-shaped substituents such as biphenyl, terphenyl, (poly)benzoic acid phenyl ester, (poly)ether, benzylideneaniline, or acenaphthoquinoxaline, or discotic substituents such as triphenylene, phthalocyanine, or azacrown, i.e., groups capable of inducing liquid crystal phase behavior. Liquid crystal compounds with rod- or plate-shaped substituents are known in the art as calamitic liquid crystals. Examples of such nematic liquid crystal monomers having a polymerizable group include the polymerizable liquid crystals described in JP-A Nos. 2003-315556 and 2004-29824, the PALIOCOLOR series (manufactured by BASF) and the RMM series (manufactured by Merck), etc. These nematic liquid crystal monomers having a polymerizable group may be used alone or in combination.

[0064] Furthermore, it is also possible to add a polymerizable compound that does not have liquid crystallinity but can react with a nematic liquid crystal monomer having a polymerizable group. Examples of such compounds include ultraviolet-curable resins. Examples of ultraviolet curable resins include dipentaerythritol hexa(meth)acrylate, a reaction product of dipentaerythritol penta(meth)acrylate and 1,6-hexamethylene-diisocyanate, a reaction product of a triisocyanate having an isocyanuric ring and pentaerythritol tri(meth)acrylate, a reaction product of pentaerythritol tri(meth)acrylate and isophorone-diisocyanate, dipentaerythritol penta(meth)acrylate, dipentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, tris(acryloxyethyl)isocyanurate, tris(meth ... tris(acryloxyethyl)isocyanurate, reaction products of glycerol triglycidyl ether and (meth)acrylic acid, caprolactone-modified tris(acryloxyethyl)isocyanurate, reaction products of trimethylolpropane triglycidyl ether and (meth)acrylic acid, triglycerol-di-(meth)acrylate, reaction products of propylene glycol-di-glycidyl ether and (meth)acrylic acid, polypropylene glycol-di-(meth)acrylate, tripropylene glycol-di-(meth)acrylate, polyethylene glycol-di-(meth)acrylate, tetraethylene glycol-di-(meth)acrylate, triethylene glycol-di-(meth)acrylate, pentaerythritol-di-(meth)acrylate, reaction products of 1,6-hexanediol-di-glycidyl ether and (meth)acrylic acid, 1,6-Hexanediol-di-(meth)acrylate, glycerol-di-(meth)acrylate, reaction products of ethylene glycol-di-glycidyl ether and (meth)acrylic acid, reaction products of diethylene glycol-di-glycidyl ether and (meth)acrylic acid, bis(acryloxyethyl)hydroxyethyl isocyanurate, bis(methacryloxyethyl)hydroxyethyl isocyanurate, reaction products of bisphenol A-di-glycidyl ether and (meth)acrylic acid, tetrahydrofurfuryl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, polypropylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, phenoxyhydroxypropyl Examples of the acrylates include methyl acrylate, ... These UV-curable resins that do not have liquid crystallinity must be added to an extent that the liquid crystal composition containing the nematic liquid crystal monomer does not lose its liquid crystallinity, and are preferably added in an amount of 0.1 to 20 parts by mass, more preferably 1.0 to 10 parts by mass, per 100 parts by mass of the nematic liquid crystal monomer having a polymerizable group.

[0065] When the nematic liquid crystal monomer having a polymerizable group and the polymerizable compound without liquid crystallinity are UV-curable, a photopolymerization initiator is added to cure the liquid crystal composition containing them with UV light. Examples of the photopolymerization initiator include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1 (Irgacure 907 manufactured by BASF), 1-hydroxycyclohexylphenyl ketone (Irgacure 184 manufactured by BASF), 4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone (Irgacure 2959 manufactured by BASF), 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one ( Acetophenone compounds such as Darocure 953 (Merck), 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one (Darocure 1116 (Merck), 2-hydroxy-2-methyl-1-phenylpropan-1-one (Irgacure 1173 (BASF)) and diethoxyacetophenone; benzoin compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether and 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651 (BASF)); benzophenone compounds such as benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide and 3,3'-dimethyl-4-methoxybenzophenone (Kayacure MBP (Nippon Kayaku)); and thioxanthone, 2-chlorothiobenzoates. Examples of the thioxanthone compounds include oxanthone (Kayacure CTX manufactured by Nippon Kayaku Co., Ltd.), 2-methylthioxanthone, 2,4-dimethylthioxanthone (Kayacure RTX manufactured by Nippon Kayaku Co., Ltd.), isopropylthioxanthone, 2,4-dichlorothioxanthone (Kayacure CTX manufactured by Nippon Kayaku Co., Ltd.), 2,4-diethylthioxanthone (Kayacure DETX manufactured by Nippon Kayaku Co., Ltd.), and 2,4-diisopropylthioxanthone (Kayacure DITX manufactured by Nippon Kayaku Co., Ltd.).Preferred examples of the photopolymerization initiator include Irgacure TPO, Irgacure TPO-L, Irgacure OXE01, Irgacure OXE02, Irgacure 1300, Irgacure 184, Irgacure 369, Irgacure 379, Irgacure 819, Irgacure 127, Irgacure 907, and Irgacure 1173 (all manufactured by BASF), and particularly preferred examples include Irgacure TPO, Irgacure TPO-L, Irgacure OXE01, Irgacure OXE02, Irgacure 1300, and Irgacure 907. These photopolymerization initiators can be used alone or in combination in any desired ratio.

[0066] When a benzophenone compound or a thioxanthone compound is used as the photopolymerization initiator, an auxiliary agent can be used in combination to promote the photopolymerization reaction. Examples of such auxiliary agents include amine compounds such as triethanolamine, methyldiethanolamine, triisopropanolamine, n-butylamine, N-methyldiethanolamine, diethylaminoethyl methacrylate, Michler's ketone, 4,4'-diethylaminophenone, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, and isoamyl 4-dimethylaminobenzoate.

[0067] The amounts of the photopolymerization initiator and auxiliary agent added are preferably within a range that does not affect the liquid crystallinity of the liquid crystal composition used to prepare the optically functional layer, and the amounts are preferably 0.5 to 10 parts by mass, more preferably 2 to 8 parts by mass, relative to 100 parts by mass of the ultraviolet-curable compound in the liquid crystal composition. The amount of the auxiliary agent is preferably 0.5 to 2 times the amount of the photopolymerization initiator.

[0068] It is also preferable to add at least one compound (hereinafter simply referred to as "additive compound") selected from the group consisting of compounds represented by the following formula (II), compounds represented by the following formula (III), and compounds represented by the following formula (IV) together with the liquid crystal compound. This further improves the heat resistance of the half-wave plate, and can further reduce the change in the retardation value of the half-wave plate even in a high-temperature atmosphere.

[0069] [ka]

[0070] In formulas (II) to (IV), R 1-1 , R 1-2 and R 1-3 R each independently represents an alkyl group having a branched structure and 5 or more carbon atoms. 1-1 , R 1-2 and R 1-3 When R is independently an alkyl group having a branched structure, the change in the retardation value of the half-wave plate in a high-temperature atmosphere is particularly small. The number of carbon atoms in R is preferably 6 or more and 18 or less. 1-1 , R 1-2 and R 1-3 are each independently a CH3-(CH2)m-CHRX- group, where RX represents an alkyl group having 1 to 5 carbon atoms, and R 1-1 , R 1-2 and R 1-3 are each independently more preferably a CH3-(CH2)m-CH(C2H5)- group, and particularly preferably a 2-ethylhexyl group or a 2-ethylbutyl group, where m represents an integer ranging from 1 to 6. In formula (III), R 3 represents a -(CH2)p- group or a phenylene group, and p represents an integer of 4 to 8. 3 When R is a phenylene group, the phenylene group may have a substituent at any of the o-, m-, and p-positions, but preferably has a substituent at the o-position. 4represents a substituted phenylene group, and the substituted phenylene group may have a substituent at any of the o-, m-, and p-positions, but preferably has a substituent at the o- and p-positions. 2 represents a -CH2-CH2- group, a -CH2-CH(CH3)- group or a -CH2-CH2-CH2- group, with a -CH2-CH2- group being preferred.

[0071] Examples of the compound represented by formula (II) include triethylene glycol-di-2-ethylhexanoate (3GO), tetraethylene glycol-di-2-ethylhexanoate (4GO), triethylene glycol-di-2-ethylbutyrate (3GH), tetraethylene glycol-di-2-ethylbutyrate, pentaethylene glycol-di-2-ethylhexanoate, octaethylene glycol-di-2-ethylhexanoate, nonaethylene glycol-di-2-ethylhexanoate, and decaethylene glycol-di-2-ethylhexanoate.

[0072] Examples of the compound represented by formula (III) include bis(2-ethylhexyl) adipate, bis(2-ethylbutyl) adipate, bis(2-ethylhexyl) azelaate, bis(2-ethylbutyl) azelaate, di-2-ethylhexyl sebacate, di-2-ethylbutyl sebacate, di-2-ethylhexyl phthalate, and di-2-ethylbutyl phthalate.

[0073] Examples of the compound represented by formula (IV) include tri-2-ethylhexyl trimellitate and tri-2-ethylbutyl trimellitate.

[0074] The compounds represented by formula (II), formula (III), and formula (IV) may be used alone or in combination of two or more. Among these, the compounds represented by formula (II) are preferred because they have excellent compatibility with the liquid crystal compound and can provide a stable retardation element. Among the compounds represented by formula (II), triethylene glycol-di-2-ethylhexanoate (3GO), tetraethylene glycol-di-2-ethylhexanoate (4GO), and triethylene glycol-di-2-ethylbutyrate (3GH) are more preferred, and triethylene glycol-di-2-ethylhexanoate (3GO) is even more preferred, because they have excellent compatibility with the liquid crystal compound and are particularly effective in suppressing changes in the retardation value of a half-wave plate under high-temperature conditions.

[0075] The content of at least one additive compound selected from the group consisting of compounds represented by formula (II), compounds represented by formula (III), and compounds represented by formula (IV) is not particularly limited, but is preferably 0.1 to 300 parts by mass, more preferably 0.5 to 50 parts by mass, even more preferably 0.8 to 30 parts by mass, and particularly preferably 1 to 15 parts by mass, relative to 100 parts by mass of the liquid crystal compound. If the content of the additive compound is less than 0.1 parts by mass, the effect of suppressing the change in the retardation value of the half-wave plate in a high-temperature atmosphere may not be obtained. On the other hand, even if the content of the additive compound exceeds 300 parts by mass, the effect of suppressing the change in the retardation value of the half-wave plate in a high-temperature atmosphere remains unchanged. Therefore, the upper limit of the content of the additive compound is preferably 300 parts by mass or less from the viewpoint of material costs.

[0076] <1 / 4 wavelength version> Depending on the design of the HUD system, a quarter-wave plate (B-2) can also be used as the optical functional layer. A quarter-wave plate is a retardation element that converts circularly polarized light into linearly polarized light. It can be obtained, for example, by uniaxially stretching a film made of polycarbonate or cycloolefin polymer so that the retardation is ¼ of the wavelength, or by orienting a horizontally aligned polymerizable liquid crystal to a thickness that results in a retardation of ¼ of the wavelength. It is also preferable that the quarter-wave plate contains the polymerizable liquid crystal layer described above. In such a case, the quarter-wave plate is composed of the polymerizable liquid crystal layer described above as a layer that converts the polarization axis and a supporting substrate on which a coating liquid forming the polymerizable liquid crystal layer is applied. However, the supporting substrate is not an essential component of the optical functional layer; the polymerizable liquid crystal layer can also be transferred to another substrate (e.g., a polyvinyl acetal resin layer or a glass plate) for use.

[0077] When the phase difference due to wavelength dispersion is large, a phase difference element called a broadband quarter-wave plate may be used as the quarter-wave plate. A broadband quarter-wave plate is a phase difference element with reduced wavelength dependency of phase difference. Examples include a phase difference element in which a half-wave plate and a quarter-wave plate with the same wavelength dispersion are stacked so that the angle between their slow axes is 60°, and a polycarbonate phase difference element (Teijin: PureAce WR-S) with reduced wavelength dependency of phase difference. Furthermore, when light is incident obliquely on the quarter-wave plate, as in a head-up display (HUD), the phase difference may change depending on the angle of incidence of the light, depending on the phase difference element. In such cases, a phase difference element with an adjusted refractive index can be used to more precisely match the phase difference, thereby suppressing the change in phase difference due to the angle of incidence. As such an example, when the refractive index in the slow axis direction in the plane of the retardation element is nx, the refractive index in the direction perpendicular to nx in the plane of the retardation element is ny, and the refractive index in the thickness direction of the retardation element is nz, the coefficient Nz shown in the above formula (4) is controlled to be preferably 0.3 to 1.0, more preferably 0.5 to 0.8.

[0078] When an optical functional layer including a quarter-wave plate is provided in the functional glass according to the present invention (described later) and the functional glass is applied to an HUD system, the optical functional layer is preferably a laminate of a (B-4) quarter-wave plate and a circularly polarized reflective layer. Specifically, the optical functional layer preferably comprises a circularly polarized reflective layer, a first quarter-wave plate laminated on one side of the circularly polarized reflective layer, and a second quarter-wave plate laminated on the other side of the circularly polarized reflective layer. A light-reflecting layer using a cholesteric liquid crystal is preferably used as the circularly polarized reflective layer. In such a configuration, the HUD system has two quarter-wave plates, of which the first quarter-wave plate is provided on the side where S-polarized or P-polarized light is incident, and the second quarter-wave plate is provided on the side where circularly polarized light transmitted through the circularly polarized reflective layer is incident. For example, if a circularly polarized light reflective layer has the ability to reflect right-handed circularly polarized light, when P-polarized light enters a first quarter-wave plate, almost none of the P-polarized light is reflected at the interface of the first quarter-wave plate and instead passes through the first quarter-wave plate. The transmitted P-polarized light is converted to right-handed circularly polarized light by the first quarter-wave plate, and a portion of this right-handed circularly polarized light is reflected by the circularly polarized light reflective layer due to the right-handed circularly polarized light conversion performance of the circularly polarized light reflective layer. The reflected right-handed circularly polarized light is then converted back to P-polarized light by the first quarter-wave plate, and this P-polarized light reaches the viewer. Furthermore, the right-handed circularly polarized light that is not reflected by the circularly polarized light reflective layer but passes through the circularly polarized light reflective layer is converted back to P-polarized light by the second quarter-wave plate, but this P-polarized light passes through the second quarter-wave plate without being reflected at the outer interface. On the other hand, when S-polarized light enters the first quarter-wave plate, it is reflected by the surface of the first quarter-wave plate, and this S-polarized light reaches the viewer. S-polarized light that is not reflected by the first quarter-wave plate and passes through it is converted to left-handed circularly polarized light by the first quarter-wave plate. This left-handed circularly polarized light is not reflected by the circularly polarized light reflective layer, which has the function of reflecting right-handed circularly polarized light, but passes through the circularly polarized light reflective layer, and is returned to its original S-polarized state by the second quarter-wave plate. This S-polarized light also passes through the second quarter-wave plate with almost no reflection at the outer interface. According to the same principle, even when the circularly polarized light reflective layer has the function of reflecting left-handed circularly polarized light, either P-polarized light or S-polarized light reaches the viewer.

[0079] The upper limit of the thickness of the quarter-wave plate is preferably 10 μm or less, more preferably 5 μm or less, from the viewpoint of the alignment of the liquid crystal. On the other hand, the lower limit of the thickness of the quarter-wave plate is preferably 0.3 μm or more, more preferably 0.5 μm or more. Furthermore, the upper limit of the thickness of the circularly polarized light reflective layer is preferably 10 μm or less, more preferably 5 μm or less, from the viewpoint of the alignment of the liquid crystal. On the other hand, the lower limit of the thickness of the circularly polarized light reflective layer is preferably 0.3 μm or more, more preferably 0.5 μm or more, from the viewpoint of the polymerizability of the liquid crystal.

[0080] (B) When the optically functional layer includes a polymerizable liquid crystal layer, the liquid crystal composition constituting the polymerizable liquid crystal layer may be coated on a supporting substrate. Such a supporting substrate is preferably transparent in the visible light region to maintain the visibility of the displayed image. Specifically, the visible light transmittance at wavelengths of 380 nm to 780 nm is preferably 50% or more, more preferably 70% or more, and even more preferably 85% or more. The supporting substrate may be colored, but is preferably uncolored or lightly colored. Furthermore, the refractive index of the supporting substrate is preferably 1.2 to 2.0, more preferably 1.4 to 1.8. The thickness of the supporting substrate may be selected appropriately depending on the application, and is preferably 5 μm to 1000 μm, more preferably 10 μm to 250 μm, and particularly preferably 15 μm to 150 μm.

[0081] The support substrate may be a single layer or a laminate of two or more layers. Examples of materials for the support substrate include triacetyl cellulose (TAC), acrylic, polycarbonate, polyvinyl chloride, polyolefin, and polyethylene terephthalate (PET). Among these, triacetyl cellulose (TAC), polyolefin, and acrylic, which have low birefringence, are preferred.

[0082] In the optical laminate according to this embodiment, it is particularly preferable that two or more (B) optical functional layers are included. In such a case, nothing is used between the optical functional layers, i.e., the optical functional layers may be directly laminated to each other, or an adhesive or pressure-sensitive adhesive layer may be used between the optical functional layers. Examples of pressure-sensitive adhesives include acrylic and rubber-based pressure-sensitive adhesives, with acrylic pressure-sensitive adhesives being preferred because of their easy adjustment of adhesion, holding power, etc. Examples of adhesives include ultraviolet-curable resin compositions and mixtures thereof. In the case of ultraviolet-curable resins, a composition containing a mixture of multiple monomers having acryloyl groups or epoxy groups can be cured and bonded by irradiating ultraviolet light in the presence of a photopolymerization initiator. Furthermore, a composition containing multiple monomers or polymers having amino groups, carboxyl groups, or hydroxyl groups can be cured and bonded by heating in the presence of a compound having an isocyanate group or melamine.

[0083] <Method of manufacturing optical functional layer> Next, a method for preparing an optical functional layer using the nematic liquid crystal monomer having a polymerizable group will be described. For example, the nematic liquid crystal monomer having a polymerizable group is dissolved in a solvent, followed by the addition of a photopolymerization initiator. The solvent is not particularly limited as long as it can dissolve the liquid crystal monomer used. Examples include cyclopentanone, toluene, methyl ethyl ketone, and methyl isobutyl ketone. Cyclopentanone and toluene are preferred. The solution is then applied to a plastic substrate, such as a PET film or TAC film, used as a support substrate, to a uniform thickness. The solution is then heated to remove the solvent, and left for a certain period of time under temperature conditions that allow the liquid crystal to align on the support substrate. Prior to application, the surface of the plastic substrate can be subjected to a rubbing treatment in the desired orientation direction, or to an orientation treatment such as forming a film of a photoalignment material that exhibits photoalignment upon polarized light irradiation on the surface of the plastic substrate and then irradiating it with polarized light, thereby achieving more uniform liquid crystal alignment. This allows the slow axis of the optical functional layer to be controlled to a desired angle and reducing the haze value of the optical functional layer. Next, while maintaining this orientation, the nematic liquid crystal monomer is irradiated with ultraviolet light from a high-pressure mercury lamp or the like to fix the orientation of the liquid crystal, thereby obtaining an optically functional layer having the desired slow axis.

[0084] [Functional Glass] The functional glass according to the present invention comprises the optical laminate and (D) a glass plate. The glass plate may be one or more, but the functional glass preferably has a structure in which the optical laminate is sandwiched between two glass plates. Such functional glass is suitable for use as a display medium in a HUD system.

[0085] When laminating the optical laminate to a glass plate, for example, a pressure-sensitive adhesive or adhesive may be applied to one or both sides of the optical laminate, and then the glass plate may be laminated to the optical laminate. There are no particular limitations on the pressure-sensitive adhesive or adhesive, but if there is a possibility of subsequent peeling, a pressure-sensitive adhesive with excellent reworkability is preferred, such as a silicone pressure-sensitive adhesive or an acrylic pressure-sensitive adhesive. The functional glass according to the present invention has a polyvinyl acetal resin layer, and therefore has excellent impact resistance.

[0086] <(D) Glass plate> The glass plate is not particularly limited as long as it has sufficient transparency to allow sufficient visibility of the forward scenery, even when the functional glass of the present invention is used as a windshield. The refractive index of the glass plate is preferably 1.2 or more and 2.0 or less, more preferably 1.4 or more and 1.8 or less. The thickness, shape, etc. of the glass plate are also not particularly limited and can be appropriately designed as long as they do not affect the reflection of display light when the functional glass is applied to a HUD system. These glass plates may also be provided on their reflective surfaces with a multilayered reflection-enhancing film or a metal thin film layer that also functions as a heat shield. These films can improve the reflectance of incident polarized light, but when the functional glass of the present invention is used as a windshield for an automobile, it is preferable to adjust the reflectance so that the visible light transmittance of the functional glass is 70% or more.

[0087] When the optical laminate of this embodiment is used, the optical laminate is placed between two glass plates and then pressed at high temperature and high pressure to obtain functional glass in which the optical laminate is placed between the two glass plates. FIG. 3 shows one embodiment of functional glass according to the present invention. The functional glass 20 shown in FIG. 3 has an optical laminate 10 sandwiched between two glass plates 201, and the optical laminate 10 corresponds to, for example, the optical laminate shown in FIG. 1 or 2. As shown in FIG. 3, when the optical laminate 10 is included in the functional glass 20, the polyvinyl acetal resin layer 101 of the optical laminate 10 also functions as a pressure-sensitive adhesive or adhesive to maintain adhesion between the glass plates 201 and the optical laminate 10.

[0088] An example of a method for producing functional glass using the optical laminate of this embodiment will be specifically described. First, two glass sheets are prepared. When the functional glass is used as a laminated glass for an automobile windshield, soda-lime glass produced by the float process is preferably used. The glass may be either transparent or green-tinted, with no particular restrictions. The thickness of these glass sheets is usually approximately 2 mm, but in response to recent demands for lightweight glass, glass sheets with slightly thinner thicknesses can also be used. The glass sheets are cut to a predetermined shape, and the glass edges are chamfered and cleaned. If a black frame or dot print is required, this is printed on the glass sheets. When a curved surface is required, such as a windshield, the glass sheets are heated to 650°C or higher, and then shaped so that the two glass sheets have the same surface shape by pressing with a mold, bending under their own weight, or the like, and the glass is cooled. At this time, slow cooling is performed because if the cooling rate is too fast, stress distribution will occur in the glass sheets and they will become tempered glass. One of the glass plates thus prepared is placed horizontally, the optical laminate according to this embodiment is placed on top of it, and then the other glass plate is placed on top. Next, the optical functional layer, polyvinyl acetal resin layer, etc. that protrude from the edge of the glass are cut and removed with a cutter. Thereafter, the sandwiched glass and optical laminate are heated to a temperature of 80 to 100°C while degassing the air present between them, thereby performing preliminary bonding. There are two methods for degassing the air: a bag method in which the glass plate / optical laminate / glass plate laminate is wrapped in a rubber bag made of heat-resistant rubber, etc., and a ring method in which only the edges of the glass plate are covered and sealed with a rubber ring. Either method may be used. After preliminary bonding is complete, the glass plate / optical laminate / glass plate laminate removed from the rubber bag, or the laminate with the rubber ring removed, is placed in an autoclave and pressurized at 10 to 15 kg / cm. 2 The glass plate is heated to 120°C to 150°C under high pressure and subjected to heat and pressure treatment under these conditions for 20 to 40 minutes. After the treatment, the glass plate is cooled to 50°C or below, the pressure is released, and the functional glass according to this embodiment, which is a laminate of glass plate / optical laminate / glass plate, is taken out from the autoclave.

[0089] The functional glass thus produced can be used as windshields, side windows, rear windows, and roof glass for standard-sized automobiles, compact automobiles, light automobiles, large special-purpose automobiles, and small special-purpose automobiles. It can also be used as windows for railway vehicles, ships, and aircraft, and as window materials for building and industrial use. It can be used by laminating or bonding with components that have UV-cutting or dimming functions.

[0090] [Head-up display system] FIG. 4 is a schematic diagram illustrating one embodiment of a HUD system according to the present invention. The HUD system shown in FIG. 4 includes a display image projection means (display) 2 that converts display light representing a display image into S-polarized or P-polarized light and emits the light; a reflecting mirror 3 that reflects the display light emitted from the display image projection means 2; and a functional glass for a head-up display (functional glass) 4 according to the present invention onto which the S-polarized or P-polarized light emitted from the display image projection means 2 is incident. The S-polarized or P-polarized light emitted from the display image projection means 2 is reflected by the reflecting mirror 3, and the reflected display light is irradiated onto the functional glass 4 that functions as a windshield. The S-polarized or P-polarized light reaches the observer 1 via an optical path 5, and the observer 1 can view a virtual image 6 of the display image. In the HUD system shown in FIG. 4, the display light emitted from the display image projection means 2 is incident on the functional glass 4 via the reflecting mirror 3, but it may also be incident directly onto the windshield from the display image projection means 2. In addition, the display image projection means 2 may emit display light showing the display image as random light, which may be reflected by the reflecting mirror 3, and the reflected light may pass through a polarizing plate before reaching the functional glass 4, thereby adjusting the polarization of the light emitted from the display image projection means 2 and irradiating the functional glass 4 with the desired polarized light.

[0091] <Angle of incidence from display projection device> In the HUD system according to the present invention, as shown in Fig. 5, when the Brewster angle of S-polarized or P-polarized light with respect to the functional glass 4 is α, the incident angle 8 at which light emitted from the display image projection means 2 is incident on the functional glass 4 as a display medium is preferably in the range of α-10° to α+10°, and more preferably in the range of α-5° to α+5°. Note that as shown in Fig. 5, the incident angle 8 refers to the angle between an axis perpendicular to the surface of the display medium (functional glass 4) and the light incident on the surface of the display medium.

[0092] In one embodiment of the HUD system of the present invention, when a half-wave plate is used as the optical functional layer, the display medium is functional glass 4, and the display light emitted from the display image projection means 2 is S-polarized light, the S-polarized light emitted from the display image projection means 2 is incident at an angle of incidence 8 in the range of α-10° to α+10°, i.e., near Brewster's angle with respect to the axis perpendicular to the surface of the functional glass 4, preferably at Brewster's angle α, thereby suppressing reflection of P-polarized light converted by the functional glass 4 from the glass plate on the exterior of the vehicle and preventing double images. In other words, when the incident angle 8 of the S-polarized light is less than α-10° or more than α+10°, the incident angle 8 of the S-polarized light deviates from near Brewster's angle, which increases the reflectance of P-polarized light converted by the half-wave plate and may cause double images.

[0093] In another embodiment of the HUD system of the present invention, the optical functional layer is a laminate of one or more circularly polarized reflective layers (cholesteric liquid crystal layers) sandwiched between two quarter-wave plates, the display medium is functional glass 4, and the display light emitted from the display image projection unit 2 is P-polarized. Because light reflected from the road surface is generally S-polarized, polarized sunglasses are designed to absorb S-polarized light. Therefore, conventional HUD systems using S-polarized light significantly reduce the visibility of the HUD display image through polarized sunglasses. On the other hand, HUD systems using P-polarized light, which allows P-polarized light to reach the viewer, can suppress the occurrence of double images and improve the visibility of the display image even when wearing polarized sunglasses. Furthermore, when the circularly polarized reflective layer is a cholesteric liquid crystal layer, the circularly polarized light passing through the circularly polarized reflective layer is converted back to P-polarized light by a second quarter-wave plate whose slow axis is positioned perpendicular to the slow axis of the first quarter-wave plate. The converted P-polarized light is also incident on the exterior glass surface of the vehicle outside the second quarter-wave plate at approximately the Brewster angle, which significantly reduces the reflectance of P-polarized light on the exterior glass surface of the vehicle outside the second quarter-wave plate, resulting in a significant improvement in the occurrence of double images.

[0094] In the head-up display system of the present invention, the polarization axis conversion performance of the half-wave plate or quarter-wave plate can be further improved by controlling the angle θ between the polarization axis of S-polarized or P-polarized light incident on the optical laminate and the slow axis of the half-wave plate or quarter-wave plate provided in the optical laminate. Details regarding each θ are as described above using formulas (5) and (6). In such cases, from the viewpoints of controllability of the slow axis of the half-wave plate or quarter-wave plate and production costs, it is particularly preferable to use a half-wave plate or quarter-wave plate including a polymerizable liquid crystal layer as the layer that converts the polarization axis. The wavelength dispersion of the above-mentioned half-wave plate or quarter-wave plate is not particularly limited as long as it is suitable for head-up display applications. However, it is desirable for the half-wave plate or quarter-wave plate to have reverse wavelength dispersion in order to accurately convert polarization over a wide wavelength range in the visible light region.

[0095] Generally, polymers exhibit normal dispersion, in which the absolute value of birefringence increases toward the short wavelength side. However, by using a liquid crystal compound whose birefringence increases toward the long wavelength side by controlling the value of birefringence Δn at each wavelength of visible light, reverse wavelength dispersion can be obtained. Furthermore, reverse wavelength dispersion can also be obtained by combining and stacking the slow axes of multiple retarders having appropriate retardation values ​​according to the wavelength dispersion characteristics of the liquid crystal compound in an appropriate positional relationship. Even in the case of a half-wave plate or a quarter-wave plate formed by stacking multiple retarders in an appropriate positional relationship, by appropriately controlling the angle θ between the polarization axis of S-polarized or P-polarized light incident on the optical laminate and the slow axis of the half-wave plate or the quarter-wave plate, as described above, the half-wave plate or the quarter-wave plate exhibits good polarization axis conversion performance, resulting in a clearer displayed image.

[0096] <Display image projection means> The display image projection means 2 used in the HUD system of the present invention is not particularly limited as long as it can emit the desired P-polarized or S-polarized light before finally reaching the functional glass 4. Examples include a liquid crystal display (LCD) and an organic light-emitting diode (OLED) display. When the display image projection means 2 is a liquid crystal display, the emitted light is usually linearly polarized, so the liquid crystal display can be used as the display image projection means 2 as is. On the other hand, when the display image projection means 2 is an OLED display, the display image projection means 2 may be composed of a light source 2A and a polarizing plate 2B capable of emitting P-polarized or S-polarized light, as shown in FIG. 6. Furthermore, when the HUD system is used in an automobile, the liquid crystal display or OLED display can be adjusted so that P-polarized or S-polarized light is emitted from the display image projection means 2 by arranging optical components such as a polarizing plate or a half-wave plate at a light exit port, such as a dashboard. Furthermore, the light source used in the display image projection means 2 is not particularly limited, and a laser light source, an LED light source, or the like can be used. Furthermore, by setting the central reflection wavelength of the retardation element constituting the optical functional layer to correspond to the emission spectrum of the light source, it is possible to more effectively project a clearer image.

[0097] <Reflector> The HUD system of the present invention may include a reflecting mirror 3 as needed. The reflecting mirror 3 is not particularly limited as long as it can reflect the display light from the display image projection means 2 toward the functional glass 4, and may be, for example, a plane mirror, a concave mirror, or the like. When a concave mirror is used as the reflecting mirror 3, the concave mirror can also magnify the display light from the display at a predetermined magnification ratio. [Example]

[0098] The present invention will be described in detail below with reference to examples. In the examples, "parts" means parts by mass. The present invention is not limited to the following examples as long as it does not deviate from the spirit of the invention. Unless otherwise specified, room temperature is defined as a temperature within the range of 20°C ± 5°C.

[0099] [Example 1] <Preparation of Coating Liquid (Liquid Crystal Composition)> A coating solution A having the composition shown in Table 1 was prepared.

[0100] [Table 1]

[0101] <Fabrication of optical functional layer> Two half-wave plates were fabricated using the prepared coating solution A according to the following procedure. The supporting substrate used was a TAC film (P960, manufactured by TacBright, Inc., thickness 60 μm) that had been rubbed using the method described in Example 1 of JP-A No. 2002-90743. The rubbing angle was set so that the angle between the longitudinal direction of the film and the slow axis of the half-wave plate (hereinafter also referred to as the "slow axis angle") was 71.5° and 26.5°, respectively.

[0102] (i) Coating Solution A was applied to the rubbed surface of the TAC film at room temperature using a wire bar so that the thickness of the resulting half-wave plate after drying would be approximately 2 μm. (ii) The resulting coating film was heated at 50°C for 2 minutes to remove the solvent and convert it into a liquid crystal phase. The liquid crystal phase was then irradiated with UV light from a high-pressure mercury lamp (Harrison Toshiba Lighting Co., Ltd.) at 120W output for 5 to 10 seconds to fix the liquid crystal phase. A polymerizable liquid crystal layer was then laminated onto the TAC film to produce a half-wave plate. The retardation values ​​of the half-wave plates were measured using an automatic birefringence meter (Oji Measurement Co., Ltd., "KOBRA-21ADH"), and two half-wave plates were obtained with retardation values ​​at 546nm of 290nm (slow axis angle 71.5°) and 250nm (slow axis angle 26.5°). (iii) For each half-wave plate prepared in (i) to (ii), the polymerizable liquid crystal layer sides were laminated together with the longitudinal direction of each film using an acrylic adhesive (SK Dyne 906, manufactured by Soken Chemical & Engineering Co., Ltd.) to prepare an optical functional layer.

[0103] The average transmittance of each half-wave plate obtained in the visible wavelength range in the front direction (incident angle 56°) was approximately 79%, and the polarized light transmittance was approximately 10%. The polarized light transmittance was measured using a Shimadzu UV-3600 ultraviolet / visible / near-infrared spectrophotometer, with the optical laminate set between parallel polarizing plates at an incident angle of 56°.

[0104] <Preparation of Polyvinyl Acetal Resin Layer> Triethylene glycol-di-2-ethylhexanoate (3GO) was blended with 100 parts by weight of polyvinyl butyral resin in the ratios shown in Table 2 (0 to 35 parts by weight). A solution of 0.2 parts by weight of 2,6-di-tert-butyl-p-cresol dissolved in methyl ethyl ketone was then added as an antioxidant. The mixture was melt-kneaded uniformly using a mixing roll. The resulting blend was then press-molded at 150°C for 30 minutes to produce polyvinyl butyral resin films (30 cm x 30 cm) with a thickness of 0.38 mm. The photoelastic coefficients of the polyvinyl butyral resin films (PVB films) containing the specified plasticizer blend ratios were measured using a spectroscopic ellipsometer (JASCO Corporation, M-220). The results are shown in Table 2.

[0105] [Table 2]

[0106] <Production of optical laminate> PVB film A, which contained 35 parts by weight of plasticizer for 100 parts by weight of polyvinyl butyral resin, and PVB film B, which contained no plasticizer (0 parts by weight) for 100 parts by weight of polyvinyl butyral resin, were each cut into a size of 10 cm long x 10 cm wide. In the prepared optical functional layer, PVB film A was placed on the TAC on the side of the 1 / 2 wavelength plate with a retardation value of 290 nm, and PVB film B was placed on the TAC on the side of the 1 / 2 wavelength plate with a retardation value of 250 nm. Then, by pressing and bonding them using a laminator, an optical laminate was prepared in which a 1 / 2 wavelength plate was placed between two PVB films A and B.

[0107] <Production of functional glass> The prepared optical laminate was placed between two glass plates of 2 mm thickness and the same size as the optical laminate, 10 cm length x 10 cm width, and then pressurized and heated to prepare functional glass. First, the optical laminate and the transparent glass plate were placed on top of a transparent glass plate in this order. This was wrapped in a rubber bag and degassed for 30 minutes in an autoclave heated to 90°C for pre-bonding. After cooling to room temperature, it was removed from the rubber bag and again heated in the autoclave at 140°C and 14 kg / cm. 2 The glass was heated and pressed under high pressure for 30 minutes, and a functional glass with a good appearance and an optical laminate inserted was produced.

[0108] <Evaluation of in-plane unevenness in polarized light transmittance> The polarized light transmittance of the resulting functional glass was measured in the wavelength range of 400 nm to 750 nm. Polarized light transmittance was measured using a Shimadzu UV-3600 ultraviolet / visible / near-infrared spectrophotometer, with the functional glass positioned between two parallel polarizing plates at an incident angle of 56°. The measurement points were the center X of the glass and point Y, 2.5 cm away from center X. The polarized light transmittance was measured at each measurement point. The results are shown in Table 3. At both measurement points, the transmittance was 6% or less in the wavelength range of 450 nm to 700 nm, and there was no significant difference in the transmittance waveform. Therefore, it was determined that there was no in-plane unevenness in polarized light transmittance (hereinafter referred to as "in-plane unevenness"). Hereinafter, the criteria for judging polarized light transmittance unevenness are as follows: if the transmittance at measurement points X and Y is both 6% or less in the wavelength range of 450 nm or more and 700 nm or less, it is evaluated as having no in-plane unevenness; and if the transmittance at measurement point X is 6% or less and the transmittance at measurement point Y is greater than 6%, it is evaluated as having in-plane unevenness.

[0109] <Production of a head-up display and evaluation of the displayed image> A head-up display was fabricated with the arrangement shown in Fig. 4. As the display image projection means 2, a liquid crystal display panel capable of emitting S-polarized light toward the functional glass 4 was installed, and the functional glass fabricated above was used as the functional glass 4. In a darkroom, the position of the optical laminate contained in the functional glass 4 was adjusted so that the angle of incidence of S-polarized light from the display image projection means 2 was the Brewster angle of the glass (approximately 56°). A glass plate on the side of the half-wave plate with a retardation value of 290 nm was placed on the display image projection means 2 side, and when an image was projected, the display image was projected brightly and clearly.

[0110] <Evaluation of in-plane unevenness of double images: Evaluation of in-plane uniformity of polarization conversion performance of half-wave plate> Using the arrangement shown in Figure 5, a horizontal line image was projected from the display image projection means 2 onto the functional glass 4 prepared above under conditions in which S-polarized light was emitted. The reflected images were visually confirmed at the center X of the glass and at measurement point Y, 2.5 cm away from the center X. At both the center X and measurement point Y, the reflected luminance of the line image at the air interface of glass plate B, located on the opposite side of glass plate A, was sufficiently low compared to the reflected luminance of the main image (i.e., the main image) at the air interface of glass plate A, which is the side of the functional glass 4 where the S-polarized light from the display image projection means 2 is incident. Therefore, the image projected onto the functional glass 4 was judged to have good image visibility over a wide range and no in-plane unevenness due to double images. Hereinafter, if the luminance of the non-main image relative to the main image at measurement point Y was higher than that at the center X, and the image projected onto the functional glass 4 was easily perceived as double, it was judged to have in-plane unevenness due to double images.

[0111] [Example 2] A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film C was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0112] [Example 3] A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film D was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0113] [Example 4] A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film E was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0114] [Example 5] A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film F was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0115] [Comparative Example 1] A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film G was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0116] Comparative Example 2 A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film H was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0117] Comparative Example 3 A functional glass and a head-up display were produced in the same manner as in Example 1, except that in the production of the optical laminate, PVB film A was used instead of PVB film B, and the polarized light transmittance and in-plane unevenness of double images were evaluated. The results are shown in Table 3.

[0118] [Table 3]

[0119] The results of Examples 1 to 5 and Comparative Examples 1 to 3 showed that when at least one of the two PVB films (polyvinyl acetal resin layers) included in the optical laminate had a photoelastic coefficient (PeA) within the specified range defined by the present invention, there was no in-plane unevenness in either polarized light transmittance or double images, resulting in excellent in-plane uniformity of performance. On the other hand, when the photoelastic coefficients of both PVB films included in the optical laminate were outside the photoelastic coefficient (PeA) range defined by the present invention, the polarized light transmittance increased at positions away from the in-plane center (glass center X) of the functional glass, resulting in in-plane unevenness in polarized light transmittance. Therefore, when S-polarized light incident on the functional glass passes through the optical laminate, much of the S-polarized light component remains without being converted to P-polarized light, which makes the S-polarized light more likely to be reflected at the air interface of the glass plate on the side opposite to the surface where the S-polarized light entered. As a result, images projected on the functional glass were easily perceived as double images, resulting in significant in-plane unevenness in double images and reduced image visibility over a wide area.

[0120] As described above, by applying the optical laminate according to the present invention to functional glass for head-up displays, S-polarized or P-polarized light incident upon projection by the head-up display can be converted uniformly and efficiently into P-polarized or S-polarized light over a wider range, and it can be seen that an optical laminate exhibiting excellent polarization conversion performance over a wide range is obtained. Furthermore, by applying the optical laminate according to the present invention to a HUD system, it is possible to view extremely clear displayed images over a wide range. [Industrial Applicability]

[0121] When the optical laminate according to the present invention is applied to a head-up display system, it eliminates unevenness in the occurrence of double images due to the projection position, i.e., it can suppress double images regardless of the projection position, allowing viewers to use the head-up display system over a wide range without stress. [Explanation of symbols]

[0122] 1 observer, 2 display image projection means, 2A light source, 2B polarizing plate, 3 reflecting mirror, 4 functional glass, 5 optical path, 6 virtual image, 8 incident angle, 10 optical laminate, 20 functional glass, 101 polyvinyl acetal resin layer, 102 optical functional layer

Claims

1. (A) at least one polyvinyl acetal resin layer having a photoelastic coefficient (PeA) in the range of the following formula (1), and (B) at least one optically functional layer, The optical laminate for a head-up display, wherein the optical functional layer is (B-1) a half-wave plate, (B-2) a quarter-wave plate, (B-3) a laminate of a half-wave plate and a circularly polarized light reflective layer, or (B-4) a laminate of a quarter-wave plate and a circularly polarized light reflective layer. [Equation 1]

2. The optical laminate according to claim 1, further comprising (C) at least one polyvinyl acetal resin layer having a photoelastic coefficient (PeC) within the range of the following formula (2): [Equation 2]

3. 3. The optical laminate according to claim 1, comprising two polyvinyl acetal resin layers having different photoelastic coefficients (Pe), wherein a ratio (PeR) of the photoelastic coefficient (Pe2) of one of the polyvinyl acetal resin layers to the photoelastic coefficient (Pe1) of the other polyvinyl acetal resin layer satisfies the following formula (3), where Pe1<Pe2: [Equation 3]

4. The optical laminate according to claim 1 , wherein the polyvinyl acetal resin layer has a thickness of 10 μm or more and 800 μm or less.

5. The optical laminate according to claim 1 , wherein the polyvinyl acetal resin layer is a polyvinyl butyral resin layer.

6. The optical laminate according to claim 1 , wherein the half-wave plate includes a polymerizable liquid crystal layer as a layer having a function of converting a polarization axis.

7. The optical laminate according to claim 1 , wherein the quarter-wave plate includes a polymerizable liquid crystal layer as a layer having a function of converting a polarization axis.

8. A functional glass for a head-up display, comprising the optical laminate according to any one of claims 1 to 7 and (D) a glass plate.

9. A head-up display system comprising the optical laminate according to any one of claims 1 to 7 or the functional glass according to claim 8.

10. 10. The head-up display system according to claim 9, comprising the functional glass, and wherein the incident angle of the light emitted from the display image projection means onto the functional glass is in the range of α-10° to α+10° with respect to Brewster's angle α.

Images