JP7260715B2 - Windshield glass and head-up display system - Google Patents

Description

The present invention relates to a windshield glass and a head-up display system using this windshield glass.

2. Description of the Related Art A so-called head-up display (head-up display system) is known that projects an image on the windshield glass of a vehicle or the like to provide information to a driver. In the following description, the head-up display system is also called "HUD". Note that HUD is an abbreviation for "Head up Display".
According to the HUD, the driver can obtain various information such as a map, driving speed, and vehicle status while looking at the external world in front of the vehicle without significantly moving the line of sight. Therefore, by using the HUD, the driver can expect to drive more safely while obtaining various kinds of information.

As is well known, in the reflection of light, the highest reflectance is obtained when s-polarized light is incident at Brewster's angle.
In response to this, in a HUD, normally, a projector projects s-polarized projection light, and the s-polarized projection light is incident on the windshield glass at an angle close to the Brewster's angle, and is reflected. Project an image.

Here, drivers often wear sunglasses while driving. As sunglasses, polarized sunglasses are known that suppress light that hinders driving, such as glare caused by reflected light from puddles on the road and the like, and glare caused by reflected light from the bonnet.
In many cases, glare caused by reflected light from puddles on the road and the like, which the driver feels is dazzling, is s-polarized light. Therefore, polarized sunglasses are usually made to block s-polarized light.
However, as described above, most of the HUD projection light is s-polarized light. Therefore, with a normal HUD, when the driver wears polarized sunglasses, the projected image cannot be observed.

A HUD using a half-mirror film that reflects p-polarized light has also been proposed to address this problem. In this HUD, a projected image is displayed by projecting p-polarized projection light from a projector and reflecting the p-polarized projection light by a half-mirror film incorporated in the windshield glass.

For example, in Patent Document 1, a non-reflective area, a reflective area composed of a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed, and a non-reflective portion and a cholesteric liquid crystal layer between the non-reflective area and the reflective area are disclosed. A half-mirror film (half-mirror) having a reflective layer including a mixed region in which a reflective portion is mixed, wherein the mixed region is characterized in that the area of the reflective portion gradually increases from the non-reflective region toward the reflective region. Are listed.
Patent Document 1 describes a windshield glass in which this half mirror film is used and laminated in the order of inner glass/interlayer film/half mirror film/intermediate film/outer glass. A half mirror film is constructed by laminating a λ/2 plate and a cholesteric liquid crystal layer (reflection layer) from the inner glass side.

In the HUD described in Patent Document 1, p-polarized projection light is incident on the windshield glass described above at Brewster's angle.
A λ/2 plate acts as a λ/2 plate when light is incident from the normal direction, but acts as a λ/4 plate when light is incident at Brewster's angle. Therefore, the p-polarized light enters the λ/2 plate, is converted into circularly polarized light, and enters the cholesteric liquid crystal layer.
As is well known, a cholesteric liquid crystal layer wavelength-selectively reflects circularly polarized light in a predetermined rotating direction. Therefore, the projection light converted into circularly polarized light by the λ/2 plate enters the cholesteric liquid crystal layer, is reflected, and enters the λ/2 plate again.
The circularly polarized light incident on the λ/2 plate is then returned to p-polarized light, and the p-polarized projected light is projected onto the position where the driver observes the projected image.

WO2018/009252

As described above, the HUD described in Patent Document 1 irradiates p-polarized projection light onto the position where the driver observes the projected image.
Therefore, with this HUD, the projected image can be observed even when the driver is wearing polarized sunglasses that block s-polarized light.

Here, the reflected light from the bonnet, puddles on the road surface, etc., which hinders driving, is mainly s-polarized light. Correspondingly, polarized sunglasses block s-polarized light, as described above.
However, when the s-polarized light entering from the outside of the windshield glass passes through the cholesteric liquid crystal layer (half mirror film) in the windshield glass, the polarization of the light changes and the p-polarized component is mixed. put away. Since polarized sunglasses block s-polarized light, this p-polarized component is transmitted through polarized sunglasses.
Therefore, in a HUD that displays a projected image with p-polarized light, the function of the polarized sunglasses for shielding the reflected light from the outside of the vehicle is impaired, which hinders driving.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art, and is a windshield glass used for a HUD, etc., which can irradiate a projected image with p-polarized light and can be projected from outside the vehicle. To provide a windshield glass which does not impair the function of polarized sunglasses for blocking s-polarized external light and is excellent in the suitability for polarized sunglasses against external light, and to provide a HUD using the windshield glass.

In order to achieve the above object, the present invention has the following configurations.
[1] A first curved glass, a polarization conversion layer having a fixed helical alignment structure of a liquid crystal compound, a cholesteric liquid crystal layer having a fixed cholesteric liquid crystal phase, and a concave surface facing the first curved glass. and a second curved glass,
A polarization conversion layer, a cholesteric liquid crystal layer and a second curved glass are provided in this order on the convex side of the first curved glass,
A windshield glass in which the pitch number x of the helical orientation structure in the polarization conversion layer and the film thickness y (unit: μm) of the polarization conversion layer satisfy all of the following formulas (a) to (c).
(a) 0.1≤x≤1.0
(b) 0.5≤y≤3.0
(c) 3000≦(1560*y)/x≦50000
[2] having a retardation layer between the cholesteric liquid crystal layer and the second curved glass;
The retardation layer has a front retardation of 50 to 170 nm at a wavelength of 550 nm, and when the direction corresponding to the vertical direction upper side of the first curved glass surface when the windshield glass is attached to the vehicle is 0 °, The windshield glass according to [1], wherein the angle of the slow axis is ±10 to 50°.
[3] The windshield glass according to [2], wherein the retardation layer has a front retardation of 50 to 140 nm at a wavelength of 550 nm.
[4] The windshield glass according to any one of [1] to [3], wherein the pitch number x and the film thickness y (unit: μm) satisfy all of the following formulas (d) to (f).
(d) 0.2≤x≤0.8
(e) 0.6≤y≤2.0
(f) 6000≦(1560*y)/x≦10000
[5] The windshield glass according to any one of [1] to [4], which has a transparent substrate between the cholesteric liquid crystal layer and the second curved glass.
[6] The windshield glass of [5], wherein the transparent substrate contains an ultraviolet absorber.
[7] The windshield glass according to any one of [1] to [6], which has an intermediate film between the first curved glass and the polarization conversion layer.
[8] The windshield glass according to any one of [1] to [7], which has a heat seal layer between the cholesteric liquid crystal layer and the second curved glass.
[9] the windshield glass according to any one of [1] to [8];
A head-up display system having a projector that irradiates projection light onto the concave surface of the first curved glass of the windshield glass.
[10] The head-up display system according to [9], wherein the projector emits p-polarized projection light.

According to the present invention, the HUD is capable of projecting (displaying) a p-polarized projected image, and at the same time, polarized sunglasses against external light that do not impair the function of polarized sunglasses for blocking s-polarized external light entering from outside the vehicle. A windshield glass with excellent aptitude and a HUD using this windshield glass are provided.

It is a figure which shows notionally an example of the windshield glass of this invention. 1 is a diagram conceptually showing an example of a HUD of the present invention; FIG. 1 is a conceptual diagram for explaining an embodiment of the present invention; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Below, the windshield glass and HUD (head-up display system) of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

As used herein, the term "to" is used to include the numerical values before and after it as lower and upper limits.

In this specification, visible light is light with a wavelength visible to the human eye among electromagnetic waves, and indicates light in the wavelength range of 380 to 780 nm. Invisible light is light in the wavelength range below 380 nm or in the wavelength range above 780 nm.
In addition, although not limited to this, among visible light, light in the wavelength range of 420 to 490 nm is blue light (B light), and light in the wavelength range of 495 to 570 nm is green light (G light). and light in the wavelength range of 620 to 750 nm is red light (R light). Furthermore, although not limited to this, ultraviolet light indicates light in the wavelength range of 100 to 380 nm among invisible light.

In this specification, s-polarized light means polarized light that oscillates in a direction orthogonal to the plane of incidence of light, and p-polarized light means polarized light that oscillates in a direction parallel to the plane of incidence of light. The plane of incidence means the plane perpendicular to the reflective surface and containing the incident and reflected rays. For s-polarized light, the plane of vibration of the electric field vector is perpendicular to the plane of incidence, and for p-polarized light, the plane of vibration of the electric field vector is parallel to the plane of incidence.

When we say "selectively" with respect to circularly polarized light, we mean that the amount of either the right-handed circularly polarized light component or the left-handed circularly polarized light component of the light is greater than the other circularly polarized light component. Specifically, when it is said to be "selective", the degree of circular polarization of light is preferably 0.3 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. It is particularly preferable that the degree of circular polarization of light is substantially 1.0. Here, the degree of circular polarization is | _{I R −IL |} /(I _R + _IL ), where IR is the intensity of the right-handed circularly polarized light component and _IL is the intensity of the left-handed circularly polarized light component. is the value to be

When we say "sense" for circularly polarized light, we mean right-handed circularly polarized light or left-handed circularly polarized light. The sense of circular polarization is right circular polarization if the tip of the electric field vector rotates clockwise as time increases, and left if it rotates counterclockwise when viewed as if the light were traveling toward you. Defined as being circularly polarized.

The term "sense" is sometimes used for the twisted direction of the helix of the cholesteric liquid crystal. When the helix direction (sense) of the cholesteric liquid crystal is right, it reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. When the sense is left, it reflects left-handed circularly polarized light and transmits right-handed circularly polarized light.

In the present specification, front retardation (front Re) is a value measured using AxoScan manufactured by Axometrics. Unless otherwise specified, the measurement wavelength is 550 nm.
The front retardation can also be measured by KOBRA 21ADH or WR (manufactured by Oji Keisoku Kiki Co., Ltd.) by allowing light of a wavelength within the visible light wavelength range to enter in the direction normal to the film. When selecting the measurement wavelength, the wavelength selection filter can be manually replaced, or the measured value can be converted by a program or the like for measurement.

As used herein, "projection image" means an image based on the projection of light from the projector being used, rather than the surrounding scenery, such as the front. The projected image is observed as a virtual image that appears to the observer beyond the projected image display portion of the windshield glass.
As used herein, "screen image" means an image displayed on a rendering device of a projector or rendered by a rendering device, such as on an intermediate image screen. An image is a real image as opposed to a virtual image.

In this specification, the "visible light transmittance" is the A light source visible light transmittance defined in JIS R 3212:2015 (automobile safety glass test method). That is, the visible light transmittance is measured with a spectrophotometer using light source A, and the transmittance of each wavelength in the range of 380 to 780 nm is measured. and the transmittance obtained by multiplying the transmittance at each wavelength by a weighting coefficient obtained from the wavelength interval and taking a weighted average.

<Windshield glass>
The windshield glass of the present invention is used for vehicles and the like, and is generally used as a windshield for vehicles such as cars and trains, aircraft, ships, two-wheeled vehicles, and playground equipment.
In the present invention, "outside the vehicle" and "inside the vehicle" refer to "outboard" and "inboard" in the case of an aircraft, and "outboard" and "inboard" in the case of a ship. Regarding this point, the expression "mounted in a vehicle" is the same.
In the HUD of the present invention, projection light is projected toward the windshield glass from the inside of the vehicle.

FIG. 1 conceptually shows an example of the windshield glass of the present invention.
All of the drawings shown below are conceptual diagrams for explaining the present invention. Therefore, the thickness, size, shape, positional relationship, etc. of each layer and each member do not necessarily match the actual product.

Windshield glass 10 shown in FIG. , and a heat seal layer 20 . The reflective layer 18 has a cholesteric liquid crystal layer. In the illustrated example, the reflective layer 18 has a green-blue reflecting cholesteric liquid crystal layer 18GB and a red reflecting cholesteric liquid crystal layer 18R as cholesteric liquid crystal layers.
The first glass 12 is the first curved glass in the present invention. Also, the second glass 14 is the second curved glass in the present invention. The second glass 14 is arranged with its concave surface facing the convex surface of the first glass 12 .
Further, the illustrated windshield glass 10 includes an intermediate film 16, a polarization conversion layer 24, a reflective layer 18, a retardation layer 28, a transparent substrate 26, a heat seal layer 20, and, on the convex surface side of the first glass 12, A second glass 14 is arranged in this order. A half-mirror film with a transparent substrate 26 is composed of the polarization conversion layer 24 , the reflection layer 18 and the retardation layer 28 .
In the following description, in the windshield glass 10, the side of the first glass 12 is also referred to as "lower" and the side of the second glass 14 is also referred to as "upper" for convenience.

In the windshield glass 10 of the present invention, the intermediate film 16, the retardation layer 28, the transparent substrate 26, and the heat seal layer 20 are provided as preferred embodiments and are not essential constituents.
That is, the windshield glass of the present invention has at least the first glass 12, the polarization conversion layer 24, the reflective layer 18, and the second glass 14, and the polarization conversion layer is provided on the convex side of the first glass 12. 24, the reflective layer 18 and the second glass 14 may be provided in this order. In this configuration, the polarization conversion layer 24 and the reflection layer 18 form a half mirror film.
Therefore, the windshield glass of the present invention may be composed only of the first glass 12, the polarization conversion layer 24, the reflective layer 18 and the second glass 14, or in addition to these, the intermediate film 16 and the retardation layer. 28, transparent substrate 26 and one or more of heat seal layer 20, as appropriate.
Which of the intermediate film 16, the retardation layer 28, the transparent substrate 26, and the heat seal layer 20 is added may be appropriately selected according to the use of the windshield glass, the required performance, the layer structure, and the like. Just do it.

<<first glass and second glass>>
As described above, the first glass 12 is the first curved glass in the present invention. Also, the second glass is the second curved glass in the present invention.
The windshield glass 10 of the present invention, which is laminated glass using the first glass 12 and the second glass 14, which are curved glasses, is curved laminated glass.
As described above, the windshield glass 10 of the present invention includes the intermediate film 16, the polarization conversion layer 24, the reflective layer 18, the retardation layer 28, the transparent substrate 26, and the heat seal layer 20 on the convex surface side of the first glass 12. , and the second glass 14 are arranged in this order.
When the general windshield glass is curved glass, the concave side of the curved surface is the inner surface of the vehicle. Therefore, in the windshield glass 10, the concave surface of the first glass 12 is the surface on the inside of the vehicle, and the convex surface of the second glass 14 is the surface on the outside of the vehicle. In the windshield glass 10 , the projection light of the HUD, which will be described later, is emitted from the concave surface side of the first glass 12 .

The shapes of the first glass 12 and the second glass 14 are not limited, and any curved glass (a glass plate having a curved surface) can be used as a windshield glass depending on the vehicle in which it is installed. shapes are available.
Therefore, the first glass 12 and the second glass 14 may be entirely curved, or may have both curved and flat surfaces. Further, the curved surfaces of the first glass 12 and the second glass 14 may have the same curvature over the entire surface, or may have curved surfaces with different curvatures.

If the first glass 12 and the second glass 14 are curved glass, a glass plate generally used for windshield glass can be used.
One example is a glass plate having a visible light transmittance of 80% or less, such as 73% and 76%, such as green glass with high heat shielding properties.

The thicknesses of the first glass 12 and the second glass 14 are not limited, and thicknesses that provide sufficient strength may be appropriately set in accordance with the materials and shapes of the glass plates.
The thickness of the first glass 12 and the second glass 14 is preferably 0.5 to 5.0 mm, more preferably 1.0 to 3.0 mm, even more preferably 2.0 to 2.3 mm.
The materials and/or thicknesses of the first glass 12 and the second glass 14 may be the same or different.

<<Intermediate film>>
An intermediate film 16 is provided on the convex surface of the first glass 12 . As described above, the intermediate film 16 is provided as a preferred embodiment, and is provided between the first glass 12 and the polarization conversion layer 24 .
The intermediate film 16 is a known intermediate film used for laminated glass used as windshield glass. Therefore, the intermediate film 16 adheres the first glass 12 and the polarization conversion layer 24 to be described later, and prevents the glass from scattering inside the vehicle and the window when receiving an impact such as when an accident occurs. It has a function of ensuring impact resistance, such as preventing an object that impacts the shield glass 10 from entering the vehicle.

As the intermediate film 16, various known intermediate films used for laminated glass used as windshield glass can be used.
As an example, the intermediate film 16 may be a resin film containing resin such as polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer, and chlorine-containing resin. The above resin is preferably the main component of the intermediate film 16 . In addition, the term "main component" refers to the most abundant component among the components forming the product, and preferably refers to the component accounting for 50% by mass or more.

Among the above resins, polyvinyl butyral and ethylene-vinyl acetate copolymer are preferred, and polyvinyl butyral is more preferred. The resin is preferably a synthetic resin.
Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol with butyraldehyde. A preferable lower limit of the degree of acetalization of polyvinyl butyral is 40%, a preferable upper limit is 85%, a more preferable lower limit is 60%, and a more preferable upper limit is 75%.

Polyvinyl alcohol is generally obtained by saponifying polyvinyl acetate, and polyvinyl alcohol having a degree of saponification of 80 to 99.8 mol % is generally used.
The preferred lower limit of the degree of polymerization of polyvinyl alcohol is 200, and the preferred upper limit is 3,000. When the degree of polymerization of polyvinyl alcohol is 200 or more, the penetration resistance of the resulting laminated glass is less likely to decrease. Good workability. A more preferable lower limit is 500, and a more preferable upper limit is 2,000.

In the windshield glass 10 of the present invention, the thickness of the intermediate film 16 is not limited. The thickness of the intermediate film 16 may be appropriately set according to the material used for forming the intermediate film 16 so as to obtain the desired impact resistance and adhesive strength.
The thickness of the intermediate film 16 is preferably 380-1500 μm.
By setting the thickness of the intermediate film 16 to 380 μm or more, it is possible to obtain sufficient impact resistance, to obtain sufficient adhesion between the first glass 12 and the polarization conversion layer 24, and to sufficiently shield the interior of the vehicle from ultraviolet rays. It is preferable in that it can be obtained in By setting the thickness of the intermediate film 16 to 1500 μm or less, it is preferable in that the windshield glass 10 can be made thinner and the weight of the windshield glass can be reduced.
The thickness of the intermediate film 16 is more preferably 500-1140 μm, even more preferably 700-800 μm.

A polarization conversion layer 24 is provided on the intermediate film 16 , that is, between the intermediate film 16 and the reflective layer 18 .
The polarization conversion layer 24 is a layer in which the helical alignment structure of the liquid crystal compound is fixed.
The polarization conversion layer 24 converts p-polarized light (linearly polarized light) incident from the side of the first glass 12 on the vehicle interior side into circularly polarized light. Also, the polarization conversion layer 24 converts the circularly polarized light reflected by the reflective layer 18 (cholesteric liquid crystal layer) into p-polarized light.
The windshield glass 10 of the present invention, by combining the polarization conversion layer 24 and the cholesteric liquid crystal layer as the reflection layer 18, makes it possible to project a p-polarized image with high brightness.
The polarization conversion layer 24 will be detailed later.

<<reflection layer>>
A reflective layer 18 is provided on the polarization conversion layer 24 .
The reflective layer 18 has a cholesteric liquid crystal layer with a fixed cholesteric liquid crystal phase. Therefore, the reflective layer 18 selectively reflects light in a specific wavelength range.
In the windshield glass 10 of the present invention, the reflective layer 18, that is, the cholesteric liquid crystal layer may be provided corresponding to the entire surface of the first glass 12 or may be provided corresponding to a part of the first glass 12. .
Considering the ease of adapting the windshield glass 10 to the HUD, the accuracy of the position where the reflective layer 18 is incorporated, etc., in the present invention, it is preferable to provide the reflective layer 18 corresponding to the entire surface of the first glass 12 .
In this regard, the same applies to the polarization conversion layer 24 and the retardation layer 28 .

The illustrated reflective layer 18 has a green-blue reflecting cholesteric liquid crystal layer 18GB that selectively reflects green light and blue light, and a red reflecting cholesteric liquid crystal layer 18R that selectively reflects red light. In the illustrated reflecting layer 18, for example, a green/blue reflecting cholesteric liquid crystal layer 18GB and a red reflecting cholesteric liquid crystal layer 18R are laminated in this order from the polarization conversion layer 24 side.
However, the windshield glass of the present invention is not limited to this, and various cholesteric liquid crystal layers and combinations of cholesteric liquid crystal layers can be used.
As an example, the windshield glass of the present invention may have only the green-blue reflecting cholesteric liquid crystal layer 18GB. Further, the windshield glass of the present invention may have two layers of a red-green reflecting cholesteric liquid crystal layer that selectively reflects red light and green light and a blue reflecting cholesteric liquid crystal layer that selectively reflects blue light. Alternatively, it may have only a red-green reflecting cholesteric liquid crystal layer.
Further, the windshield glass of the present invention may have three layers of cholesteric liquid crystal layers: a red-reflecting cholesteric liquid crystal layer, a green-reflecting cholesteric liquid crystal layer that selectively reflects green light, and a blue-reflecting cholesteric liquid crystal layer. . In addition, the windshield glass of the present invention may have only one layer of a red-reflecting cholesteric liquid crystal layer, a green-reflecting cholesteric liquid crystal layer, and a blue-reflecting cholesteric liquid crystal layer, or may have a combination thereof selected as appropriate. It may have two layers.
Furthermore, the windshield glass of the present invention may have a cholesteric liquid crystal layer that reflects all of blue light, green light and red light with a single layer.

Here, the cholesteric liquid crystal layer is known to shift the central wavelength of selective reflection to the short wavelength side with respect to oblique light. The above shift of the central wavelength of reflection to the short wave side is called blue shift. With oblique light, blue shift occurs in the cholesteric liquid crystal layer due to the fact that the optical path length difference between each layer becomes small in optical interference. Therefore, blue shift occurs when observed from an oblique direction.
Therefore, in the cholesteric liquid crystal layer constituting the reflective layer 18, it is desirable to previously correct the shift of the central wavelength of reflection to the short wavelength side so that the central wavelength of reflection in front of the selective reflection layer is shifted to the long wavelength side. The central wavelength of the oblique light is the central wavelength of the oblique light = the central wavelength at the front x cos θ, where θ is the angle from the front when the oblique light propagates through the selective reflection layer. It is possible to adopt a configuration in which the center wavelength is shifted. The wavelength range of the reflective layer 18 described above is set in consideration of the blue shift.

[Cholesteric liquid crystal layer]
A cholesteric liquid crystal layer is a layer in which a cholesteric liquid crystal phase is fixed.
The cholesteric liquid crystal layer may be any layer as long as the orientation of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. A cholesteric liquid crystal layer is typically formed by aligning a polymerizable liquid crystal compound in a cholesteric liquid crystal phase, and then polymerizing and curing by ultraviolet irradiation, heating, or the like to form a layer having no fluidity, and at the same time, Any layer may be used as long as it is changed to a state in which the orientation is not changed by an external field or external force. In the cholesteric liquid crystal layer, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained in the layer, and the liquid crystal compound in the layer may no longer exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound may be polymerized by a curing reaction and no longer have liquid crystallinity.

It is known that a cholesteric liquid crystal phase selectively reflects either right-handed circularly polarized light or left-handed circularly polarized light and transmits the other sense circularly polarized light. .
Many films formed from a composition containing a polymerizable liquid crystal compound are conventionally known as films containing a layer in which a cholesteric liquid crystal phase exhibiting selective reflection of circularly polarized light is fixed. You can refer to the technology.

The central wavelength of selective reflection by the cholesteric liquid crystal layer (selective reflection central wavelength) λ depends on the pitch P (= helical period) of the helical alignment structure in the cholesteric liquid crystal phase, and the average refractive index n and λ = n of the cholesteric liquid crystal layer It follows the relationship of ×P. As can be seen from this equation, the selective reflection center wavelength can be adjusted by adjusting the n value and/or the P value.
The pitch P of the helical alignment structure (one helical pitch) is, in other words, the length in the direction of the helical axis corresponding to one turn of the helical structure. is the length in the direction of the helical axis that rotates 360°. The helical axis direction of a normal cholesteric liquid crystal layer coincides with the thickness direction of the cholesteric liquid crystal layer.

As an example, the selective reflection center wavelength and half width of the cholesteric liquid crystal layer can be obtained as follows.
When the reflection spectrum of the cholesteric liquid crystal layer is measured from the normal direction using a spectrophotometer (manufactured by JASCO Corporation, V-670), a transmittance drop peak is observed in the selective reflection band. Of the two wavelengths that have an intermediate (average) transmittance between the minimum transmittance of this peak and the transmittance before decrease, the wavelength on the short wavelength side is λ _l (nm), and the wavelength on the long wavelength side is λ _h (nm), the selective reflection central wavelength λ and the half width Δλ can be expressed by the following equations.
λ=( _λl + _λh )/2Δλ=( _λh − _λl )
The selective reflection center wavelength obtained as described above substantially coincides with the wavelength at the centroid position of the reflection peak of the circularly polarized reflection spectrum measured from the normal direction of the cholesteric liquid crystal layer.

In the HUD of the present invention, which will be described later, the reflectance on the surface of the first glass 12 can be reduced by using the windshield glass 10 so that light is obliquely incident thereon.
At this time, the light obliquely enters the cholesteric liquid crystal layer forming the reflective layer 18 as well. For example, light incident at an angle of 45° to 70° with respect to the normal to the windshield glass 10 in air with a refractive index of 1 passes through the cholesteric liquid crystal layer with a refractive index of about 1.61 at an angle of about 26° to 36°. to pass through. In this case, the reflected wavelength shifts to the short wavelength side.
In a cholesteric liquid crystal layer with a selective reflection center wavelength of wavelength λ, the selective reflection center wavelength when a light ray passes at an angle of _θ2 with respect to the normal direction of the cholesteric liquid crystal layer (spiral axis direction of the cholesteric liquid crystal layer) is When the wavelength is λ _d , the wavelength λ _d is expressed by the following formula.
λ _d =λ×cos θ ₂

Therefore, a cholesteric liquid crystal layer having a central wavelength of selective reflection in the range of 650 to 780 nm when θ ₂ is 26 to 36° can reflect projection light in the range of 520 to 695 nm.
Since such a wavelength range is a wavelength range with high luminosity, it has a high degree of contribution to the luminance of a projected image, and as a result, a projected image with high luminance can be realized.

Since the helical pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used together with the polymerizable liquid crystal compound and the concentration thereof added, a desired pitch can be obtained by adjusting these. As for the method for measuring the sense and pitch of the helix, the method described in "Introduction to Liquid Crystal Chemistry Experiments" edited by the Japan Liquid Crystal Society, published by Sigma Publishing, 2007, page 46, and "Liquid Crystal Handbook" Liquid Crystal Handbook Editing Committee Maruzen, page 196 is used. be able to.

Moreover, in the windshield glass of the present invention, the cholesteric liquid crystal layers are preferably arranged in order from the one having the shortest central wavelength of selective reflection when viewed from the viewing side, ie, the inside of the vehicle.

For each cholesteric liquid crystal layer, a cholesteric liquid crystal layer with either right or left helix sense is used. The sense of circularly polarized light reflected by the cholesteric liquid crystal layer (the direction of rotation of the circularly polarized light) matches the sense of the helix.
In the case of having a plurality of cholesteric liquid crystal layers with different selective reflection center wavelengths, the helical sense of each cholesteric liquid crystal layer may be the same or different. However, it is preferable that all of the plurality of cholesteric liquid crystal layers have the same helical sense, that is, the rotating direction of the selectively reflected circularly polarized light.

When the windshield glass 10 has a plurality of cholesteric liquid crystal layers as the reflective layer 18, the cholesteric liquid crystal layers exhibiting selective reflection in the same or overlapping wavelength ranges should not include cholesteric liquid crystal layers with different spiral senses. is preferred. This is to prevent the transmittance in a specific wavelength range from dropping below 50%, for example.

The half width Δλ (nm) of the selective reflection band indicating selective reflection depends on the birefringence Δn of the liquid crystal compound and the pitch P described above, and follows the relationship Δλ=Δn×P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. The Δn can be adjusted by adjusting the type or mixing ratio of the polymerizable liquid crystal compound, or by controlling the temperature during orientation fixation.
In order to form one type of cholesteric liquid crystal layer having the same center wavelength of selective reflection, a plurality of cholesteric liquid crystal layers having the same pitch P and the same spiral sense may be laminated. By stacking cholesteric liquid crystal layers with the same pitch P and the same helical sense, the circular polarization selectivity can be increased at a particular wavelength.

The reflective layer 18 preferably has a cholesteric liquid crystal layer with a reflection wavelength band within the wavelength range of 540 to 850 nm and a half width of 150 nm or more. By setting the half-value width of the cholesteric liquid crystal layer to 150 nm or more, the reflective layer 18 becomes a selective reflective layer that selectively reflects broadband light. As a result, when the windshield glass 10 is used for a HUD or the like, the brightness of the image can be increased.

When laminating a plurality of cholesteric liquid crystal layers in the reflective layer 18, a separately prepared cholesteric liquid crystal layer may be laminated using an adhesive or the like, or the previous cholesteric liquid crystal layer formed by a method described later may be laminated. A liquid crystal composition containing a polymerizable liquid crystal compound or the like may be applied directly to the surface of the layer, and the alignment and fixing steps may be repeated, but the latter is preferred.
By forming the next cholesteric liquid crystal layer directly on the surface of the previously formed cholesteric liquid crystal layer, the alignment direction of the liquid crystal molecules on the air interface side of the previously formed cholesteric liquid crystal layer and the cholesteric liquid crystal layer formed thereon are changed. This is because the alignment directions of the liquid crystal molecules on the lower side are matched, and the polarizing property of the laminate of the cholesteric liquid crystal layers is improved. In addition, it is because interference unevenness that can be caused by thickness unevenness of the adhesive layer is not observed.

The thickness of the cholesteric liquid crystal layer is preferably 0.5 to 10 μm, more preferably 1.0 to 8.0 μm, even more preferably 1.5 to 6.0 μm.
Further, when the windshield glass 10 has a plurality of cholesteric liquid crystal layers, the total thickness of the cholesteric liquid crystal layers is preferably 2.0 to 30 μm, more preferably 2.5 to 25 μm, and more preferably 3.0 to 20 μm. is more preferred.
In the windshield glass 10, a high visible light transmittance can be maintained without reducing the thickness of the cholesteric liquid crystal layer.

(Method for Forming Cholesteric Liquid Crystal Layer)
The material and method for forming the cholesteric liquid crystal layer will be described below.
Examples of materials used for forming the cholesteric liquid crystal layer include a liquid crystal composition (coating liquid) containing a polymerizable liquid crystal compound and a chiral agent (optically active compound). If necessary, a liquid crystal composition mixed with a surfactant, a polymerization initiator, and the like and dissolved in a solvent or the like is applied to the support, the alignment layer, the underlying cholesteric liquid crystal layer, etc., and after cholesteric orientation aging. can be fixed by curing the liquid crystal composition to form a cholesteric liquid crystal layer.

(Polymerizable liquid crystal compound)
The polymerizable liquid crystal compound may be a rod-like liquid crystal compound or a discotic liquid crystal compound, but is preferably a rod-like liquid crystal compound.
An example of the rod-like polymerizable liquid crystal compound forming the cholesteric liquid crystal layer is a rod-like nematic liquid crystal compound. Rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and alkoxy-substituted phenylpyrimidines. , phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used. Not only low-molecular-weight liquid crystal compounds but also high-molecular liquid-crystal compounds can be used.

A polymerizable liquid crystal compound is obtained by introducing a polymerizable group into a liquid crystal compound. Examples of polymerizable groups include unsaturated polymerizable groups, epoxy groups, and aziridinyl groups, with unsaturated polymerizable groups being preferred, and ethylenically unsaturated polymerizable groups being particularly preferred. Polymerizable groups can be introduced into molecules of liquid crystal compounds by various methods. The number of polymerizable groups possessed by the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3, in one molecule.
Examples of polymerizable liquid crystal compounds are described in Makromol. Chem. , 190, 2255 (1989); Advanced Materials 5, 107 (1993); U.S. Pat. No. 4,683,327; U.S. Pat. No. 5,622,648; U.S. Pat. , WO95/24455, WO97/00600, WO98/23580, WO98/52905, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-A-11-80081, and , and compounds described in JP-A-2001-328973. Two or more types of polymerizable liquid crystal compounds may be used in combination. When two or more kinds of polymerizable liquid crystal compounds are used together, the alignment temperature can be lowered.

Further, the amount of the polymerizable liquid crystal compound added in the liquid crystal composition is preferably 80 to 99.9% by mass, and preferably 85 to 99.5% by mass, based on the solid content mass (mass excluding the solvent) of the liquid crystal composition. % is more preferable, and 90 to 99% by mass is particularly preferable.

In order to improve the visible light transmittance, the green blue reflecting cholesteric liquid crystal layer 18GB may have a low Δn. The low Δn green-blue reflective cholesteric liquid crystal layer 18GB can be formed using a low Δn polymerizable liquid crystal compound. The low Δn polymerizable liquid crystal compound will be specifically described below.

(Low Δn polymerizable liquid crystal compound)
A narrow-band selective reflection layer can be obtained by forming a cholesteric liquid crystal phase using a low Δn polymerizable liquid crystal compound and fixing it to a film. Examples of low Δn polymerizable liquid crystal compounds include compounds described in WO2015/115390, WO2015/147243, WO2016/035873, JP-A-2015-163596, and JP-A-2016-53149. The description of WO2016/047648 can also be referred to for the liquid crystal composition that provides a selective reflection layer with a small half-value width.

The liquid crystal compound is also preferably a polymerizable compound represented by the following formula (I) described in WO2016/047648.

In formula (I), A represents an optionally substituted phenylene group or an optionally substituted trans-1,4-cyclohexylene group, L is a single bond, —CH ₂ O-, -OCH ₂ -, -(CH ₂ ) ₂ OC(=O)-, -C(=O)O(CH ₂ ) ₂ -, -C(=O)O-, -OC(=O) -, -OC(=O)O-, -CH=CH-C(=O)O-, and -OC(=O)-CH=CH-, and m represents a linking group selected from the group consisting of represents an integer of 3 to 12, and Sp ¹ and Sp ² are each independently a single bond, a linear or branched alkylene group having 1 to 20 carbon atoms, and a linear or branched alkylene group having 1 to 20 carbon atoms; one or more of -CH ₂ - are -O-, -S-, -NH-, -N(CH ₃ )-, -C(=O)-, -OC(=O)-, or - represents a linking group selected from the group consisting of groups substituted with C(=O)O-, wherein Q ¹ and Q ² are each independently a hydrogen atom or represented by formulas Q-1 to Q-5 below; wherein either one of Q ¹ and Q ² represents a polymerizable group.

The phenylene group in formula (I) is preferably a 1,4-phenylene group.
Regarding the phenylene group and the trans-1,4-cyclohexylene group, the substituent when "optionally having a substituent" is not particularly limited, and examples thereof include alkyl groups, cycloalkyl groups, alkoxy groups, alkyl ether groups, amido groups, amino groups, halogen atoms, and substituents selected from the group consisting of a combination of two or more of the above substituents. Examples of substituents include substituents represented by -C(=O)-X ³ -Sp ³ -Q ³ described later. The phenylene group and trans-1,4-cyclohexylene group may have 1 to 4 substituents. When having two or more substituents, the two or more substituents may be the same or different.

Alkyl groups may be linear or branched. The number of carbon atoms in the alkyl group is preferably 1-30, more preferably 1-10, even more preferably 1-6. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and neopentyl. 1,1-dimethylpropyl, n-hexyl, isohexyl, linear or branched heptyl, octyl, nonyl, decyl, undecyl or dodecyl radicals. The above description regarding alkyl groups also applies to alkoxy groups containing alkyl groups. Further, specific examples of the alkylene group when referred to as an alkylene group include a divalent group obtained by removing one arbitrary hydrogen atom in each of the examples of the above-mentioned alkyl groups, and the like. Halogen atoms include fluorine, chlorine, bromine, and iodine atoms.

The number of carbon atoms in the cycloalkyl group is preferably 3 to 20, more preferably 5 or more, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl groups.

Substituents which the phenylene group and the trans-1,4-cyclohexylene group may have are particularly the group consisting of an alkyl group, an alkoxy group, and -C(=O)-X ³ -Sp ³ -Q ³ Substituents selected from are preferred. Here, X ³ represents a single bond, —O—, —S—, or —N(Sp ⁴ —Q ⁴ )—, or represents a nitrogen atom forming a ring structure together with Q ³ and Sp ³ show. Sp ³ and Sp ⁴ are each independently a single bond, a linear or branched alkylene group having 1 to 20 carbon atoms, and a linear or branched alkylene group having 1 to 20 carbon atoms, and one or more of - CH ₂ - is -O-, -S-, -NH-, -N(CH ₃ )-, -C(=O)-, -OC(=O)-, or -C(=O)O- A linking group selected from the group consisting of substituted groups is shown.

Each of Q ³ and Q ⁴ is independently a hydrogen atom, a cycloalkyl group, or a cycloalkyl group in which one or more —CH ₂ — are —O—, —S—, —NH—, —N(CH ₃ )-, -C(=O)-, -OC(=O)-, or a group substituted with -C(=O)O-, or a group represented by formulas Q-1 to Q-5 represents any polymerizable group selected from the group consisting of

one or more -CH ₂ - in the cycloalkyl group is -O-, -S-, -NH-, -N(CH ₃ )-, -C(=O)-, -OC(=O); Specific examples of groups substituted with - or -C(=O)O- include a tetrahydrofuranyl group, a pyrrolidinyl group, an imidazolidinyl group, a pyrazolidinyl group, a piperidyl group, a piperazinyl group, and a morphonyl group. . The substitution position is not particularly limited. Among these, a tetrahydrofuranyl group is preferred, and a 2-tetrahydrofuranyl group is particularly preferred.

In formula (I), L is a single bond, -CH ₂ O-, -OCH _2- , -(CH ₂ ) ₂ OC(=O)-, -C(=O)O(CH ₂ ) ₂ -,- C(=O)O-, -OC(=O)-, -OC(=O)O-, -CH=CH-C(=O)O-, and -OC(=O)-CH=CH represents a linking group selected from the group consisting of -. L is preferably -C(=O)O- or -OC(=O)-. m−1 Ls may be the same or different.

Sp ¹ and Sp ² are each independently a single bond, a linear or branched alkylene group having 1 to 20 carbon atoms, and a linear or branched alkylene group having 1 to 20 carbon atoms, and one or more of - CH ₂ - is -O-, -S-, -NH-, -N(CH ₃ )-, -C(=O)-, -OC(=O)-, or -C(=O)O- A linking group selected from the group consisting of substituted groups is shown. Each of Sp ¹ and Sp ² is independently a 1 carbon atom having a linking group selected from the group consisting of -O-, -OC(=O)-, and -C(=O)O- at both ends. A group selected from the group consisting of straight-chain alkylene groups of from to 10, -OC(=O)-, -C(=O)O-, -O-, and straight-chain alkylene groups of 1 to 10 carbon atoms is preferably a linking group constituted by combining one or two or more of and is preferably a linear alkylene group having 1 to 10 carbon atoms and having —O— attached to both ends.

Q ¹ and Q ² each independently represents a hydrogen atom or a polymerizable group selected from the group consisting of the groups represented by the above formulas Q-1 to Q-5, provided that Q ¹ and Q ² Either one represents a polymerizable group.
As the polymerizable group, an acryloyl group (formula Q-1) or a methacryloyl group (formula Q-2) is preferred.

In formula (I), m represents an integer of 3-12. m is preferably an integer of 3 to 9, more preferably an integer of 3 to 7, and even more preferably an integer of 3 to 5.

The polymerizable compound represented by formula (I) has at least one optionally substituted phenylene group as A and an optionally substituted trans-1,4-cyclohexylene group. It is preferable to include at least one. The polymerizable compound represented by formula (I) preferably contains 1 to 4 trans-1,4-cyclohexylene groups which may have a substituent as A, and preferably contains 1 to 3 groups. is more preferred, and 2 or 3 is even more preferred. Further, the polymerizable compound represented by the formula (I) preferably contains one or more phenylene groups which may have a substituent as A, more preferably contains 1 to 4 groups, 1 to It is more preferable to contain 3, and it is particularly preferable to contain 2 or 3.

In formula (I), when mc is the number obtained by dividing the number of trans-1,4-cyclohexylene groups represented by A by m, 0.1<mc<0.9 is preferable, and 0.3< mc<0.8 is more preferred, and 0.5<mc<0.7 is even more preferred. The polymerizable compound represented by the formula (I) having a liquid crystal composition satisfying 0.5<mc<0.7 and the polymerizable compound represented by the formula (I) satisfying 0.1<mc<0.3 It is also preferred to include

Specific examples of the polymerizable compound represented by formula (I) include, in addition to the compounds described in paragraphs 0051 to 0058 of WO2016/047648, JP-A-2013-112631, JP-A-2010-70543, Japanese Patent No. 4725516, WO2015/115390, WO2015/147243, WO2016/035873, JP-A-2015-163596, and compounds described in JP-A-2016-53149.

(Chiral Agent: Optically Active Compound)
A chiral agent has a function of inducing a helical alignment structure of a cholesteric liquid crystal phase. The chiral compound may be selected according to the purpose, since the helical sense or helical pitch induced by the compound differs.
The chiral agent is not particularly limited, and known compounds can be used. Examples of chiral agents include Liquid Crystal Device Handbook (Chapter 3, Section 4-3, Chiral Agents for TN and STN, p. Examples include compounds described in JP-A-2002-302487, JP-A-2002-80478, JP-A-2002-80851, JP-A-2010-181852, and JP-A-2014-034581.

A chiral agent generally contains an asymmetric carbon atom, but an axially chiral compound or planar asymmetric compound that does not contain an asymmetric carbon atom can also be used as a chiral agent. Examples of axially or planarly chiral compounds include binaphthyl, helicene, paracyclophane, and derivatives thereof.
The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral agent are formed by the polymerization reaction of the polymerizable chiral agent and the polymerizable liquid crystal compound. A polymer having repeating units can be formed. In this aspect, the polymerizable group possessed by the polymerizable chiral agent is preferably the same type of group as the polymerizable group possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. Especially preferred.
Also, the chiral agent may be a liquid crystal compound.

As the chiral agent, isosorbide derivatives, isomannide derivatives, binaphthyl derivatives, and the like can be preferably used. As the isosorbide derivative, a commercially available product such as LC756 manufactured by BASF may be used.
The content of the chiral agent in the liquid crystal composition is preferably 0.01 to 200 mol %, more preferably 1 to 30 mol % of the amount of the polymerizable liquid crystal compound. In addition, the content of the chiral agent in the liquid crystal composition intends the concentration (% by mass) of the chiral agent with respect to the total solid content in the composition.

(Polymerization initiator)
The liquid crystal composition preferably contains a polymerization initiator. In the embodiment in which the polymerization reaction is advanced by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator capable of initiating the polymerization reaction by ultraviolet irradiation.
Examples of photoinitiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbons substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), triarylimidazole dimers and p-aminophenyl ketone combination (described in US Pat. No. 3,549,367), acridine and phenazine compound (described in JP-A-60-105667, US Pat. No. 4,239,850), acylphosphine oxide compound (JP-B-63-40799, JP-B-5-29234, JP-A-10-95788, JP-A-10-29997, JP-A-2001-233842, JP-A-2000-80068, JP-A-2006-342166, JP-A 2013-114249, JP 2014-137466, JP 4223071, JP 2010-262028, JP 2014-500852), oxime compound (JP 2000-66385, Patent No. No. 4,454,067) and oxadiazole compounds (described in US Pat. No. 4,212,970). For example, paragraphs 0500 to 0547 of JP-A-2012-208494 can also be referred to.

As the polymerization initiator, it is also preferable to use an acylphosphine oxide compound or an oxime compound.
As the acylphosphine oxide compound, for example, a commercial product, IRGACURE810 (compound name: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide) manufactured by BASF Japan, can be used. Examples of oxime compounds include IRGACURE OXE01 (manufactured by BASF), IRGACURE OXE02 (manufactured by BASF), TR-PBG-304 (manufactured by Changzhou Tenryu Electric New Materials Co., Ltd.), Adeka Arkles NCI-831, and Adeka Arkles NCI-930. (manufactured by ADEKA), and ADEKA Arkles NCI-831 (manufactured by ADEKA).
Only one polymerization initiator may be used, or two or more polymerization initiators may be used in combination.
The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 5% by mass, based on the content of the polymerizable liquid crystal compound.

(crosslinking agent)
The liquid crystal composition may optionally contain a cross-linking agent in order to improve film strength and durability after curing. As the cross-linking agent, one that is cured by ultraviolet rays, heat, humidity, or the like can be preferably used.
The cross-linking agent is not particularly limited and can be appropriately selected depending on the purpose. Examples of cross-linking agents include polyfunctional acrylate compounds such as trimethylolpropane tri (meth) acrylate and pentaerythritol tri (meth) acrylate; epoxy compounds such as glycidyl (meth) acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate], 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret type isocyanate; polyoxazoline compounds having chains; alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane; Also, a known catalyst can be used depending on the reactivity of the cross-linking agent, and productivity can be improved in addition to the enhancement of membrane strength and durability. These may be used individually by 1 type, and may use 2 or more types together.
The content of the cross-linking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass. By setting the content of the cross-linking agent to 3% by mass or more, the effect of improving the cross-linking density can be obtained, and by setting the content of the cross-linking agent to 20% by mass or less, the decrease in stability of the cholesteric liquid crystal layer can be prevented. can be prevented.
In addition, "(meth)acrylate" is used in the sense of "one or both of acrylate and methacrylate".

(Orientation control agent)
An alignment control agent may be added to the liquid crystal composition to contribute to stably or rapidly forming a planar alignment cholesteric liquid crystal layer. Examples of alignment control agents include fluorine (meth)acrylate polymers described in paragraphs [0018] to [0043] of JP-A-2007-272185, paragraphs [0031] to [0031] of JP-A-2012-203237. 0034] and the like, compounds represented by formulas (I) to (IV), and compounds described in JP-A-2013-113913.
As the alignment control agent, one type may be used alone, or two or more types may be used in combination.

The amount of the alignment control agent added in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and more preferably 0.02 to 1% based on the total mass of the polymerizable liquid crystal compound. % by weight is particularly preferred.

(Other additives)
In addition, the liquid crystal composition may contain at least one selected from various additives such as a surfactant for adjusting the surface tension of the coating film to make the thickness uniform, and a polymerizable monomer. . In addition, if necessary, the liquid crystal composition may further contain polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, metal oxide fine particles, etc. to the extent that the optical performance is not reduced. can be added at

The cholesteric liquid crystal layer is a liquid crystal composition obtained by dissolving a polymerizable liquid crystal compound and a chiral agent, and optionally a polymerization initiator, a surfactant, and the like in a solvent, and a transparent base material 26 and a retardation layer, which will be described later. 28. It is coated on an alignment film or a previously prepared cholesteric liquid crystal layer or the like and dried to obtain a coating film. A cholesteric liquid crystal layer with fixed regularity can be formed.
A laminated film composed of a plurality of cholesteric liquid crystal layers can be formed by repeating the above-described manufacturing process of the cholesteric liquid crystal layer.

(solvent)
The solvent used for preparing the liquid crystal composition is not particularly limited and can be appropriately selected according to the purpose, but organic solvents are preferably used.
The organic solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters and ethers and the like. These may be used individually by 1 type, and may use 2 or more types together. Among these, ketones are particularly preferred in consideration of the load on the environment.

(coating, orientation, polymerization)
The method of applying the liquid crystal composition to the support, the alignment layer, the underlying cholesteric liquid crystal layer, etc. is not particularly limited and can be appropriately selected according to the purpose. Examples of coating methods include wire bar coating, curtain coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spin coating, dip coating, spray coating, and slide coating. law, etc. It can also be carried out by transferring a liquid crystal composition separately coated on a support.
The liquid crystal molecules are aligned by heating the applied liquid crystal composition. The heating temperature is preferably 200° C. or lower, more preferably 130° C. or lower. By this orientation treatment, an optical thin film is obtained in which the polymerizable liquid crystal compound is twisted so as to have a helical axis in a direction substantially perpendicular to the film surface.

By further polymerizing the oriented liquid crystal compound, the liquid crystal composition can be cured. Polymerization may be either thermal polymerization or photopolymerization using light irradiation, but photopolymerization is preferred. It is preferable to use ultraviolet rays for light irradiation. The irradiation energy is preferably 20 mJ/cm ² to 50 J/cm ² , more preferably 100 to 1,500 mJ/cm ² .
In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions or under a nitrogen atmosphere. The irradiation ultraviolet wavelength is preferably 350 to 430 nm. From the viewpoint of stability, the polymerization reaction rate is preferably as high as 70% or more, more preferably 80% or more. The polymerization reaction rate can be determined by measuring the consumption rate of the polymerizable functional groups by infrared absorption spectrum measurement.

<<polarization conversion layer>>
The windshield glass 10 of the present invention comprises a curved first glass 12, a convex surface side, a polarization conversion layer 24, a reflective layer 18 having the cholesteric liquid crystal layer described above, and a second glass 14, arranged in this order. have.
As will be described later, in the HUD of the present invention, the projector irradiates p-polarized projection light as a preferred embodiment to enter the windshield glass 10 .
On the other hand, the windshield glass 10 of the present invention reflects the projected light by the reflective layer 18 having a cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed. As described above, the cholesteric liquid crystal layer basically selectively reflects right-handed circularly polarized light or left-handed circularly polarized light.
The polarization conversion layer 24 converts p-polarized light (linearly polarized light) emitted from the projector into right-handed circularly polarized light or left-handed circularly polarized light that is selectively reflected by the cholesteric liquid crystal layer.

The polarization conversion layer 24 is a layer in which the helical alignment structure of the liquid crystal compound is fixed, and the pitch number x of the helical alignment structure and the film thickness y [μm] are represented by the following relational expressions (a) to (c). It satisfies all of
(a) 0.1≤x≤1.0
(b) 0.5≤y≤3.0
(c) 3000≦(1560*y)/x≦50000
As in the cholesteric liquid crystal layer described above, in the helical alignment structure of the liquid crystal compound that constitutes the polarization conversion layer 24, the pitch of the helical alignment structure (1 pitch of the spiral) is the length in the direction of the helical axis corresponding to one turn of the spiral. Yes, in other words, it is the length in the helical axis direction in which the director of the liquid crystal compound (long axis direction in the case of rod-like liquid crystal) rotates 360°.
That is, the number of pitches of 1 in the helical alignment structure of the liquid crystal compound is one turn of the spiral. In other words, the pitch number is 1 when the director of the liquid crystal compound constituting the polarization conversion layer 24 is rotated by 360°.

Such a polarization conversion layer 24 has a thickness of 0.5 to 3 μm and has a helical orientation structure with a pitch number of 0.1 to 1 pitch within this thickness.
That is, in the polarization conversion layer 24, the pitch of the helical alignment structure has a length corresponding to the pitch P of the cholesteric liquid crystal layer whose selective reflection central wavelength is in the long wavelength infrared region. Such a polarization conversion layer 24 expresses high optical rotatory power and birefringence with respect to visible light, which has a short wavelength relative to the infrared region.
Therefore, the polarization conversion layer 24 can convert p-polarized light (linearly polarized light) incident from the first glass 12 side into right-handed circularly polarized light or left-handed circularly polarized light that is selectively reflected by the reflective layer 18 . Also, the polarization conversion layer 24 converts the circularly polarized light reflected by the reflective layer 18 back to p-polarized light, and can irradiate the viewing position of the driver with projection light.

As described above, many of the so-called glare components that enter from the outside of the windshield glass of a vehicle, such as reflected light from a puddle, reflected light from the windshield glass of an oncoming vehicle, and reflected light from the hood, are s Polarization. Therefore, polarized sunglasses are designed to block s-polarized light.
Therefore, with a conventional HUD that projects s-polarized light, the projected light from the HUD cannot be observed when the driver wears polarized sunglasses.
In contrast, according to the windshield glass 10 and the HUD of the present invention, the position where the driver observes the projected image can be illuminated with p-polarized projection light. Therefore, according to the windshield glass 10 of the present invention, a p-polarized projected image can be projected, so even when the driver wears polarized sunglasses, the projected image of the HUD can be properly observed.

In addition, the windshield glass 10 of the present invention not only makes it possible to observe the image projected by the HUD while wearing polarized sunglasses, but also has good suitability for polarized sunglasses against glare incident from outside the vehicle. .

In the HUD, as described in Patent Document 1, a half-mirror film that combines a cholesteric liquid crystal layer and a retardation layer such as a λ/2 plate is used as a configuration that enables projection of p-polarized light. A configuration using shield glass is known.
As described above, this windshield glass converts incident p-polarized light into circularly polarized light with the retardation layer, reflects this circularly polarized light with the cholesteric liquid crystal layer, and converts the reflected light back into p-polarized light with the retardation layer. illuminate as projection light. As a result, even when the driver is wearing polarized sunglasses, the projected image of the HUD can be observed.

When polarized light other than the reflected component is incident on the cholesteric liquid crystal layer and is transmitted through the layer, the polarization state changes.
As described above, the glare component entering the windshield glass from the outside is s-polarized light. Therefore, the s-polarized light transmitted through the cholesteric liquid crystal layer that selectively reflects the circularly polarized light corresponding to the p-polarized light ideally becomes circularly polarized light in the rotation direction corresponding to the s-polarized light. This circularly polarized light is then converted back into s-polarized light by the retardation layer. Therefore, s-polarized light, which is a glare component entering the windshield glass from the outside, can be blocked by using polarized sunglasses.

However, the s-polarized light incident on the windshield glass from the outside is incident on the windshield glass at various angles in addition to the component incident on the cholesteric liquid crystal layer of the windshield glass from the normal direction. Therefore, in a HUD that projects p-polarized light by a conventional retardation layer and a cholesteric liquid crystal layer, as shown in Patent Document 1, the s-polarized light that enters from the outside and passes through the cholesteric liquid crystal layer is not circularly polarized light. It becomes elliptically polarized.
When such elliptically polarized light is transmitted through the retardation layer, the transmitted light includes not only s-polarized light but also p-polarized light. Since p-polarized light cannot be blocked by polarized sunglasses, it passes through polarized sunglasses.
As a result, in a conventional HUD that projects p-polarized light, the function of polarized sunglasses to block glare reflected light, which is mainly composed of s-polarized light, is impaired, which hinders driving. That is, the conventional windshield glass that projects p-polarized light and uses a half-mirror film using a retardation layer and a circularly polarized light reflecting layer, as disclosed in Patent Document 1, has low suitability for polarized sunglasses against external light.

On the other hand, the windshield glass of the present invention is not a retardation layer generally used as an element for converting p-polarized light (linearly polarized light) into circularly polarized light, but has a helical orientation structure of a liquid crystal compound as described above. is fixed in the polarization conversion layer 24 .
The windshield glass of the present invention has such a polarization conversion layer 24 on the inner side of the vehicle than the reflective layer 18 , ie, the cholesteric liquid crystal layer, so that the light enters from outside the vehicle and is converted from s-polarized light by the reflective layer 18 . The converted p-polarized component can be converted back to s-polarized light.
That is, according to the windshield glass 10 of the present invention, s-polarized light entering from the outside of the vehicle and causing glare can pass through while maintaining the state of s-polarized light. Therefore, according to the windshield glass 10 of the present invention, it is possible to block s-polarized light incident from the outside of the vehicle, which causes glare, with polarized sunglasses, which will be described later in Examples, and exhibits excellent suitability for polarized sunglasses against external light. .

The direction of rotation (sense of spiral) of the helical alignment structure in the polarization conversion layer 24 may be set according to the direction of rotation of the circularly polarized light selectively reflected by the cholesteric liquid crystal layer constituting the reflective layer 18 .
For example, when the cholesteric liquid crystal layer selectively reflects right-handed circularly polarized light, the spiral direction of the polarization conversion layer 24 is clockwise toward the reflective layer 18 . Conversely, when the cholesteric liquid crystal layer selectively reflects left-handed circularly polarized light, the spiral direction of the polarization conversion layer 24 is counterclockwise toward the reflective layer 18 .

As described above, in the windshield glass 10 of the present invention, the pitch number x of the helical orientation structure and the film thickness y of the polarization conversion layer 24 satisfy all of the relational expressions (a) to (c).
Relational expression (a) is "0.1≤x≤1.0".
If the pitch number x of the helical orientation structure is less than 0.1, problems such as insufficient optical rotation and birefringence will occur.
On the other hand, if the pitch number x of the helical orientation structure exceeds 1.0, the optical rotatory power and birefringence are excessive, resulting in problems such as failure to obtain desired circularly polarized light.

The relational expression (b) is "0.5≤y≤3.0".
If the thickness y of the polarization conversion layer 24 is less than 0.5 μm, the film thickness is too thin, resulting in problems such as insufficient optical rotation and birefringence.
If the thickness y of the polarization conversion layer 24 exceeds 3.0 μm, the optical rotatory power and birefringence are excessive, resulting in problems such as failure to obtain desired elliptically polarized light.

The relational expression (c) is "3000≤(1560*y)/x≤50000".
If "(1560*y)/x", in which the pitch number x and the thickness y [μm] of the helical orientation structure of the polarization conversion layer 24 are parameters, is less than 3000, the optical rotation is excessive and the desired polarized light cannot be obtained. Inconvenience such as
If "(1560*y)/x" exceeds 50,000, the optical rotatory power is insufficient, resulting in problems such as failure to obtain desired polarized light.

In the windshield glass 10 of the present invention, the polarization conversion layer 24 preferably satisfies all of the following relational expressions (d) to (f).
(d) 0.2≤x≤0.8
(e) 0.6≤y≤2.0
(f) 6000≦(1560*y)/x≦10000

That is, it is preferable that the polarization conversion layer 24 has a longer pitch P of the helical orientation structure and a smaller pitch number x.
Specifically, the polarization conversion layer 24 preferably has a spiral pitch P equal to the pitch P of the cholesteric liquid crystal layer whose selective reflection center wavelength is in the long wavelength infrared region, and the number of pitches x is small. More specifically, the polarization conversion layer 24 preferably has a spiral pitch P equal to the pitch P of the cholesteric liquid crystal layer having a selective reflection central wavelength of 3000 to 8000 nm, and the pitch number x is small.
In such a polarization conversion layer 24, the selective reflection central wavelength corresponding to the pitch P is much longer than that of visible light, so that the above-described optical rotation and birefringence with respect to visible light are more preferably exhibited. .

Such a polarization conversion layer 24 can be basically formed in the same manner as the cholesteric liquid crystal layer described above.
However, when forming the polarization conversion layer 24, it is preferable that the pitch number x and the film thickness y [μm] of the helical orientation structure in the polarization conversion layer 24 satisfy all the relational expressions (a) to (c). It is necessary to adjust the liquid crystal compound to be used, the chiral agent to be used, the amount of the chiral agent added, the film thickness, etc. so as to satisfy all of the relational expressions (d) to (f).

<<retardation layer>>
In the illustrated windshield glass 10 , a retardation layer 28 is provided on the reflective layer 18 . As described above, the retardation layer 28 is provided as a preferred embodiment, and is provided between the reflective layer 18 (cholesteric liquid crystal layer) and the second glass 14 . When the windshield glass has the transparent substrate 26 and the heat seal layer 20, the retardation layer 28 is preferably provided closer to the reflective layer 18 than both, as shown in the drawing.
In the present invention, the retardation layer 28 has a front retardation of 50 to 170 nm, preferably 50 to 140 nm, at a wavelength of 550 nm. Further, the retardation layer 28 has a slow axis of ± The angle is 10 to 50°.
3, which will be described later, the direction of the arrow H is the vertical direction, the upward direction of the arrow H is 0°, and the arrow Sa is the slow axis. The angle α should be ±10 to 50°.

As described above, the windshield glass 10 of the present invention has the polarization conversion layer 24 on the vehicle interior side of the reflective layer 18 (cholesteric liquid crystal layer). It has good suitability for polarized sunglasses against external light, which can be maintained and transmitted.
As a preferred embodiment, the windshield glass 10 of the present invention has the retardation layer 28, so that s-polarized light incident from the outside of the vehicle, which causes glare, can be transmitted while maintaining the s-polarized light more preferably. It is possible to further improve the suitability of polarized sunglasses for

As described above, most of the so-called glare components entering from outside the vehicle, such as reflected light from puddles, reflected light from the windshield of oncoming vehicles, and reflected light from the hood, are s-polarized light. Therefore, polarized sunglasses are designed to block s-polarized light.
However, when the s-polarized light entering from outside the vehicle passes through the cholesteric liquid crystal layer forming the reflective layer 18, the polarization of the light changes and the p-polarized component is mixed.
Since polarized sunglasses block s-polarized light, this p-polarized component is transmitted through polarized sunglasses. Therefore, in a conventional HUD that displays a projected image with p-polarized light, the function of polarized sunglasses to block the glare of reflected light incident from outside the vehicle is impaired, which poses a problem that hinders driving.

In contrast, the windshield glass 10 of the present invention preferably has a retardation layer 28 between the reflective layer 18 , ie, the cholesteric liquid crystal layer, and the second glass 14 . As a result, s-polarized light entering from outside the vehicle and causing glare enters the retardation layer 28 before entering the cholesteric liquid crystal layer.
The glaring s-polarized light incident on the retardation layer 28 is converted into elliptically polarized light with a rotating direction corresponding to the s-polarized light due to the phase difference of the retardation layer 28 .
The elliptically polarized light transmitted through the retardation layer 28 is then incident on the reflective layer 18, ie, the cholesteric liquid crystal layer. The elliptically polarized light converted from the s-polarized light passes through the cholesteric liquid crystal layer and is converted into circularly polarized light with a rotating direction corresponding to the s-polarized light because the direction of rotation of the elliptical polarized light is not a component reflected by the cholesteric liquid crystal layer. This circularly polarized light is then converted into s-polarized light by passing through the polarization conversion layer 24 and passes through the windshield glass 10 .
That is, since the windshield glass 10 of the present invention has the retardation layer 28, the glaring s-polarized light entering the windshield glass from outside the vehicle is more preferably transmitted as s-polarized light. can. Therefore, by including the retardation layer 28 in the windshield glass 10 of the present invention, it is possible to more preferably improve the suitability of polarized sunglasses for external light in a HUD that projects p-polarized light.

The retardation layer 28 used in the windshield glass 10 of the present invention has a front retardation of 50 to 170 nm, preferably 50 to 140 nm, at a wavelength of 550 nm.
When the front retardation is 50 to 170 nm, preferably 50 to 140 nm, the birefringence is appropriate, and the s-polarized light of external light can be converted into appropriate elliptically polarized light.
The front retardation of the retardation layer 28 is more preferably 70 to 130 nm, still more preferably 90 to 130 nm, and particularly preferably 90 to 120 nm.

Further, the retardation layer 28 used in the windshield glass 10 of the present invention has a slow axis angle of ±10 to 50°.
If the angle of the slow axis is ±10 to 50°, the s-polarized light of the external light can be converted into an appropriate elliptically polarized light, which is preferable.
The angle of the slow axis is preferably ±15 to 48°, more preferably ±30 to 45°.

The "+"/"-" angle of the slow axis of the retardation layer 28 is determined by the twisting direction (sense) of the spiral of the cholesteric liquid crystal layer, that is, the rotating direction of the selectively reflected circularly polarized light.
Specifically, when the cholesteric liquid crystal layer selectively reflects right-handed circularly polarized light, the angle of the slow axis is "+", and when it selectively reflects left-handed circularly polarized light, it is "-".
The angle of the slow axis of the retardation layer 28 is "+" for clockwise rotation and "-" plus for counterclockwise rotation with respect to 0°.

In the windshield glass 10 of the present invention, the retardation layer 28 is not limited and can be appropriately selected depending on the purpose.
As the retardation layer 28, for example, a stretched polycarbonate film, a stretched norbornene-based polymer film, an oriented transparent film containing inorganic particles having birefringence such as strontium carbonate, and an inorganic dielectric film on a support. Examples include a thin film obtained by oblique vapor deposition, a film obtained by uniaxially aligning a polymerizable liquid crystal compound and fixing its orientation, and a film obtained by uniaxially aligning a liquid crystal compound and fixing its orientation.

Among them, a film in which a polymerizable liquid crystal compound is uniaxially oriented and oriented and fixed is preferably exemplified as the retardation layer 28 .
As an example, such a retardation layer 28 is formed by applying a liquid crystal composition containing a polymerizable liquid crystal compound to the surface of a temporary support or an alignment layer, where the polymerizable liquid crystal compound in the liquid crystal composition is nematic in a liquid crystal state. After forming in orientation, it can be fixed by curing and formed.
Formation of the retardation layer 28 in this case can be carried out in the same manner as the formation of the cholesteric liquid crystal layer described above, except that the chiral agent is not added to the liquid crystal composition. However, the heating temperature is preferably 50 to 120.degree. C., more preferably 60 to 100.degree.

The retardation layer 28 is obtained by coating a composition containing a polymer liquid crystal compound on the surface of a temporary support, an alignment layer, or the like, forming a nematic alignment in a liquid crystal state, and then fixing the alignment by cooling. It may be a layer that can be

Although the thickness of the retardation layer 28 is not limited, it is preferably 0.2 to 300 μm, more preferably 0.5 to 150 μm, even more preferably 1.0 to 80 μm. The thickness of the retardation layer 28 formed from the liquid crystal composition is not particularly limited, but is preferably 0.2 to 10 μm, more preferably 0.5 to 5.0 μm, and further preferably 0.7 to 2.0 μm. preferable.

Instead of the windshield glass and the retardation layer 28 of the present invention, a layer in which the helically oriented structure of the liquid crystal compound is fixed, like the polarization conversion layer 24 described above, may be provided.
Also in this case, the suitability of polarized sunglasses for external light can be improved.

<<transparent substrate>>
In the illustrated windshield glass 10 , a transparent substrate 26 is provided on the retardation layer 28 .
As described above, the transparent substrate 26 is provided as a preferred embodiment, and is provided between the reflective layer 18 (cholesteric liquid crystal layer) and the second glass 14 . When the windshield glass 10 has the retardation layer 28 as in the illustrated example, the transparent substrate 26 is preferably provided between the retardation layer 28 and the second glass 14 .

The windshield glass 10 of the present invention has a transparent base material 26, so that the reflective layer 18 (cholesteric liquid crystal layer) is formed using the transparent base material 26 as a base material, and the polarization conversion layer 24 is formed on the reflective layer 18. can be formed. Alternatively, the windshield glass 10 has a transparent substrate 26, the retardation layer 28 is formed on the transparent substrate 26, the reflective layer 18 is formed thereon, and the polarization conversion layer 24 is formed on the reflective layer 18. can be formed. The reflective layer 18 and the retardation layer 28 may be formed after the transparent substrate 26 is subjected to orientation treatment.
In addition, since the transparent base material 26 is provided, a heat seal layer 20, which will be described later, is provided on the opposite side of the transparent base material 26 from the reflective layer 18, and the reflective layer 18 and the like are attached to the second glass 14 by the heat seal layer 20. can be affixed to

The material for forming the transparent base material 26 is not limited, and various materials can be used as long as they can ensure sufficient transparency.
Examples include resin materials such as triacetyl cellulose (TAC) and copolyester (coPEN) of 70 naphthalate/30 terephthalate (mol %).

The thickness of the transparent base material 26 is not limited, and the thickness that ensures sufficient strength as a base material may be appropriately set according to the material forming the transparent base material 26 .
The thickness of the transparent substrate 26 is preferably 10-250 μm, more preferably 15-90 μm.

In the windshield glass 10, the transparent substrate 26 may be subjected to orientation treatment. The alignment treatment also includes formation of an alignment film.
The orientation treatment method is not limited, and various known methods can be used. Examples include rubbing treatment, oblique vapor deposition of inorganic compounds, formation of layers with microgrooves, and organic compounds (e.g., ω-tricosanoic acid, dioctadecylmethylammonium chloride) using the Langmuir-Blodgett method (LB film). and methyl stearate) are available.

The transparent base material 26 may contain an ultraviolet absorber as needed.
The outside light incident on the windshield glass 10 contains ultraviolet rays. The ultraviolet rays deteriorate the reflective layer 18 (cholesteric liquid crystal layer), and as a result, the reflectance of the projected light is lowered and the color of the reflected light is changed.
On the other hand, since the transparent base material 26 contains an ultraviolet absorber, deterioration of the reflective layer 18 due to ultraviolet rays can be prevented, and the light resistance of the windshield glass 10 can be improved.
In addition, in the windshield glass 10 of the present invention, the intermediate film 16 may have an ultraviolet absorber, if necessary.

The ultraviolet absorbent used in the present invention is not limited, and various known ultraviolet absorbents can be used.
As the ultraviolet absorber, for example, ultraviolet absorbers described in JP-A-2012-056995, JP-A-2006-328277, and JP-A-2012-31313 can be preferably used.

Moreover, there is no limitation on the wavelength range of ultraviolet rays that the ultraviolet absorber absorbs.
As the ultraviolet absorber, an ultraviolet absorber having a maximum absorption wavelength in the wavelength range of 300 to 380 nm is preferably used. More preferably, an ultraviolet absorbent having a maximum absorption wavelength in the wavelength range of 300 to 360 nm is used.

The amount of the UV absorber added to the reflective layer 18 and the heat seal layer 20 is also not limited, and the amount may be appropriately set according to the UV absorber to be used to obtain the desired UV absorbance.

The method of forming the transparent substrate 26 containing the ultraviolet absorber is not limited, and various known methods can be used.
As an example, an ultraviolet absorber may be added to and mixed with a molten resin material before the transparent base material 26 is formed into a sheet.
In addition, such an ultraviolet absorber may be added to the retardation layer 28 and/or the heat seal layer 20 to be described later, if necessary.

<<Heat seal layer>>
In the illustrated windshield glass 10 , the heat seal layer 20 is provided on the transparent substrate 26 .
As described above, the heat seal layer 20 is provided as a preferred embodiment, and is provided between the reflective layer 18 (cholesteric liquid crystal layer) and the second glass 14 . More specifically, the heat seal layer 20 is provided in contact with the vehicle interior surface of the second glass 14, and the second glass 14, the transparent substrate 26 or the retardation layer 28 or the reflective layer 18 (cholesteric liquid crystal layer ) is attached.

As the heat seal layer 20, various layers containing known thermoplastic resin as a main component can be used. The heat seal layer 20 is preferably transparent. Also, the thermoplastic resin is preferably an amorphous resin.
As such a thermoplastic resin, a resin selected from the group consisting of a polyvinyl acetal resin typified by polyvinyl butyral (PVB) resin, an ethylene-vinyl acetate copolymer, and a chlorine-containing resin can be used.
Among the resins described above, polyvinyl acetal resins and ethylene-vinyl acetate copolymers typified by polyvinyl butyral resins are preferably exemplified, and polyvinyl acetal resins typified by polyvinyl butyral resins (also referred to as alkylacetalized polyvinyl alcohol) are more preferred. preferable. The resin is preferably a synthetic resin.
Polyvinyl butyral can be obtained by acetalizing polyvinyl alcohol with butyraldehyde. The preferred lower limit of the degree of acetalization of the polyvinyl acetal resin typified by the polyvinyl butyral resin described above is 40%, the preferred upper limit is 85%, the more preferred lower limit is 60%, and the more preferred upper limit is 80%.

Polyvinyl alcohol, which is a raw material for these resins, is usually obtained by saponifying polyvinyl acetate, and polyvinyl alcohol having a degree of saponification of 80 to 99.8 mol % is generally used.
Moreover, the preferable lower limit of the degree of polymerization of polyvinyl alcohol is 200, and the preferable upper limit thereof is 10,000. When the degree of polymerization of polyvinyl alcohol is 200 or more, the penetration resistance of the resulting laminated glass is less likely to decrease. Good workability. A more preferable lower limit is 500, and a more preferable upper limit is 5,000. The degree of polymerization as used herein means an average degree of polymerization.

Polyvinyl acetal resins preferably used for the heat seal layer 20 include, for example, KS-10, KS-1, KS-3, KS-5 and BL-5 manufactured by Sekisui Chemical Co., Ltd. These polyvinyl acetal resins easily form a mixed layer with the transparent support when coated on the transparent support.
Moreover, in order to apply a thin layer coating of the heat seal layer 20, it is important that the coating liquid has a low viscosity. From that point of view, the calculated molecular weight is preferably 10,000 or more and 50,000 or less, and KS-10 and KS-1 are preferable. In the present invention, the calculated molecular weight is defined as a value obtained by multiplying the average degree of polymerization of polyvinyl alcohol as a raw material by the molecular weight of the acetalized unit.

It is also preferable that the heat seal layer 20 contains, in addition to the polyvinyl acetal resin, a cross-linking agent that cross-links the polyvinyl alcohol units in the polyvinyl acetal resin structure.
Examples of the cross-linking agent include epoxy-based additives, and compounds having two or more epoxy groups in one molecule are particularly preferred, and compounds represented by the following general formula (EP1) are preferred.
Ep—CH ₂ —O—(R—O) _n —CH ₂ —Ep (EP1)
In general formula (EP1) above, Ep is an epoxy group, R is an alkylene group having 2 to 4 carbon atoms, and n is 1 to 30. However, when n is 2 or more, a plurality of R may be the same or different.
Specific examples of the compounds represented by the above general formula (EP1) include Denacol EX-810, 811, 821, 830, 832, 841, 850, 851, 861, 911, 920, 931 manufactured by Nagase ChemteX Corporation, and , 941 and the like.

When an epoxy-based additive is used as a cross-linking agent, a cationic polymerization initiator (photoacid generator) that is an onium salt composed of a light-absorbing cation moiety and an anion moiety that is an acid generation source can be used. A sulfonium salt or iodonium salt cationic polymerization initiator can be used. An iodonium-based cationic polymerization initiator is particularly preferred.

The heat seal layer 20 is preferably produced using a coating composition.
The coating composition forming the heat seal layer 20 preferably contains at least one solvent. As the solvent for the coating composition forming the heat seal layer 20, a solvent that dissolves the thermoplastic resin contained in the heat seal layer 20 is preferable.
For example, when the thermoplastic resin contained in the heat seal layer 20 is polyvinyl butyral, alcohols; aromatic hydrocarbons such as methanol, ethanol, isopropyl alcohol, butanol, isobutyl alcohol, and diacetone alcohol; toluene, and Glycol ethers such as xylene; Ketones such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, and cellosolve acetate; Amides such as acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, diisobutyl ketone, and isophorone; N,N-dimethyl Esters such as acetamide, N,N-dimethylformamide and N-methyl-2-pyrrolidone; Ethers such as methyl formate, methyl acetate, ethyl acetate, butyl acetate and ethyl lactate; Tetrahydrofuran, 1,4- Halogenated hydrocarbons, such as dioxane, dioxolane, diisopropyl ether, and ethyl ether; Nitrogen-containing compounds, such as methylene chloride, chloroform, and tetrachloroethane; Nitromethane, acetonitrile, N-methylpyrrolidone, and N,N-dimethyl formamide and the like, glycols; methyl glycol and methyl glycol acetate and the like; others; dimethyl sulfoxide, propylene carbonate and water and the like, or mixtures thereof.

In the windshield glass 10 of the present invention, the thickness of the heat-sealing layer 20 is not limited, and depending on the material forming the heat-sealing layer 20, the necessary adhesive force can be obtained and sufficient transparency can be obtained. The thickness may be appropriately set.
The thickness of the heat seal layer 20 is preferably 0.2 to 45 μm.
By setting the thickness of the heat seal layer 20 to 0.2 μm or more, it is preferable in terms of obtaining sufficient adhesive strength.
By setting the thickness of the heat seal layer 20 to 45 μm or less, it is possible to prevent the reflective layer 18 from developing so-called orange peel, which is preferable.
The thickness of the heat seal layer 20 is more preferably 0.5-40 μm, more preferably 1-20 μm.

<<Method of making windshield glass>>
The windshield glass 10 of the present invention can basically be produced according to known windshield glass (laminated glass) having an intermediate film and a half mirror film.
As an example, first, the retardation layer 28 is formed on one surface of the transparent substrate 26 . Prior to the formation of the retardation layer 28, the surface of the transparent substrate 26 on which the retardation layer 28 is formed may be subjected to an alignment treatment such as rubbing.
Next, the cholesteric liquid crystal layer is formed on the surface of the retardation layer 28 as described above to form the reflective layer 18, and the polarization conversion layer 24 is formed on the surface of the reflective layer 18 as described above. A half mirror film having a transparent substrate 26 is produced.
Further, a heat seal layer 20 is formed on the surface of the transparent base material 26 opposite to the surface on which the reflective layer 18 and the like are formed using, for example, a coating composition to form a half-mirror film structure.

An intermediate film 16 is provided on the convex surface side of the first glass 12, the structure is laminated on the surface of the intermediate film 16 with the polarization conversion layer 24 facing the intermediate film 16, and the heat seal layer 20 of the structure is provided on the concave surface side. are brought into contact with each other to laminate the second glass 14 .
As a result, the intermediate film 16, the polarization conversion layer 24, the reflective layer 18, the retardation layer 28, the transparent substrate 26, the heat seal layer 20, and the second glass 14 are arranged in this order on the convex surface of the first glass 12. A laminated laminate is formed. Next, the laminated body is heated at about 90° C. under vacuum and temporarily pressure-bonded, and then subjected to heat-pressure bonding treatment at 110° C. or higher under a high pressure of 1.0 MPa or more using an autoclave to obtain the windshield of the present invention. Make glass.
The processing conditions for the thermocompression bonding are not limited, and may be appropriately set according to the forming materials and configurations of the intermediate film 16, the reflective layer 18, the heat seal layer 20, and the like.

A windshield glass without at least one layer of the intermediate film 16, the transparent base material 26, the retardation layer 28 and the heat seal layer 20 can basically be produced in the same manner.
For example, the windshield glass without the heat seal layer 20, the transparent base material 26, and the retardation layer 28 is subjected to alignment treatment such as rubbing treatment on one surface of the peelable temporary support, if necessary, and then the cholesteric liquid crystal Layers are formed to form a reflective layer 18, and a polarization conversion layer 24 is further formed on the surface of the reflective layer 18 to produce a half mirror film with a temporary support.
An intermediate film 16 is provided on the convex side of the first glass 12 , and a half mirror film with a temporary support is laminated on the surface of the intermediate film 16 with the polarization conversion layer 24 facing the intermediate film 16 . Then, the peelable temporary support is peeled off.
Furthermore, the second glass 14 is laminated with the concave side facing the reflective layer.
As a result, a laminate is formed in which the first glass 12, the intermediate film 16, the polarization conversion layer 24, the reflective layer 18 and the second glass 14 are laminated in this order. Next, the windshield glass of the present invention is produced by subjecting this laminate to heat-press bonding using an autoclave or the like.

<<HUD (head-up display (system))>>
FIG. 2 conceptually shows an example of the HUD of the present invention.
A HUD 30 shown in FIG. 2 has the windshield glass 10 of the present invention described above and a projector 32 .

The projector 32 shown in FIG. 2 includes an image forming section 34 , an intermediate image screen 36 , a mirror 38 and a concave mirror 40 .

In the HUD 30 shown in FIG. 2 , the projection light projected by the projector 32 passes through a transmissive window 46 provided on the dashboard 42 of the vehicle in which the HUD 30 is mounted, and enters the windshield glass 10 as indicated by the dashed line. Then, it is reflected by the reflective layer 18 and observed by the driver D.
In the illustrated HUD, the driver D observes a virtual image projected on the windshield glass 10, as in a known HUD.

The image forming section 34 has an LCD 50 (Liquid Crystal Display) and a projection lens 52 .
Both the LCD 50 and the projection lens 52 are known objects used in projectors for HUDs. The image forming section 34 projects the image displayed by the LCD 50 onto the intermediate image screen 36 through the projection lens 52 .
In the projector 32, the intermediate image screen 36 converts the image into a real image, and the mirror 38 and the concave mirror 40 reflect the real image onto a predetermined optical path. As described above, this reflected light passes through the transmissive window 46 provided on the dashboard 42, enters the windshield glass 10 and is reflected, and the projected image is observed by the driver D (a dashed line reference).

The LCD 50 preferably displays a p-polarized image (projected image). That is, in a preferred embodiment of the HUD 30 of the present invention, the projector 32 emits p-polarized projection light.
Therefore, when the LCD 50 does not display p-polarized projection light, for example, a polarizing plate is provided in the optical path of the projection light from the LCD 50 to the concave mirror 40 to convert the projection light from the LCD 50 into p-polarization. It is preferable to provide
Alternatively, a polarizing plate may be provided outside the projector 32 , that is, in the middle of the optical path of the projected light from the concave mirror 40 to the windshield glass 10 to convert the projected light from the LCD 50 into p-polarized light.
The above points are the same when using various image forming means to be described later.

As described above, the windshield glass 10 converts p-polarized light into circularly polarized light by the polarization conversion layer 24, reflects the circularly polarized light by the reflective layer 18, and converts the circularly polarized light back to p-polarized light by the polarization conversion layer 24. . Thereby, the windshield glass 10 selectively reflects p-polarized light as a preferred embodiment.
Therefore, by emitting polarized projection light from the projector 32p, a p-polarized projection image can be projected, and the image projected by the HUD 30 can be observed even when the driver D is wearing polarized sunglasses. becomes possible.

An example of the polarizing plate is a polarizing plate in which thin films having different refractive index anisotropy are laminated. As a polarizing plate in which thin films having different refractive index anisotropy are laminated, for example, one described in JP-A-9-506837 can be used. Specifically, a wide variety of materials can be used to form polarizers when processed under conditions selected to obtain refractive index relationships.
In general, it is necessary that one of the first materials has a different refractive index in the chosen direction than the second material. This refractive index difference can be achieved in a variety of ways, including stretching, extrusion, or coating during film formation or after film formation. Additionally, it is preferred that the two materials have similar rheological properties (eg, melt viscosity) so that they can be coextruded.
A commercial product may be used as the polarizing plate in which thin films having different refractive index anisotropy are laminated. As a commercially available product, a laminate of a reflective polarizing plate and a temporary support may be used. Examples of commercially available products include DBEF (manufactured by 3M) and APF (Advanced Polarizing Film (manufactured by 3M)).
As the polarizing plate, a general linearly polarizing reflector such as an absorption polarizing plate containing an iodine compound and a reflective polarizing plate such as a wire grid can be used.

In the projector constituting the HUD of the present invention, the image forming section 34 is not limited to the LCD 50, and various known image forming means used in the HUD projector can be used.
As an example, HUD projectors such as fluorescent display tubes, LCOS (Liquid Crystal on Silicon) that uses liquid crystal, organic electroluminescence (organic EL) displays, and DLP (Digital Light Processing) that uses DMD (Digital Micromirror Device), etc. Various known imaging means used in imagers are available. In these image forming means, similarly to the LCD 50, the projected image is projected onto the intermediate image screen 36 by the projection lens.

The image forming means of the image forming unit 34 emits a light beam modulated according to the formed image from a light source, combines the R light, the G light and the B light according to necessity, and then emits the light beam. is p-polarized and two-dimensionally scanned by an optical deflector to form a projected image.
Modulation of the light beam according to the image to be projected may be performed by directly modulating the light source or by using an external light modulator.
Examples of light sources include LEDs (Light Emitting Diodes, light emitting diodes, organic light emitting diodes (including OLEDs (Organic Light Emitting Diodes)), discharge tubes, and laser light sources.
Examples of the two-dimensional optical deflector include a galvanometer mirror (galvanometer mirror), a combination of a galvanometer mirror and a polygon mirror, and MEMS (Micro Electro Mechanical Systems). Among them, MEMS is preferably used. The scanning method is not limited, and known light beam scanning methods such as random scanning and raster scanning can be used. Among them, raster scanning is preferably exemplified.

The projection light emitted from the image forming section 34 is then converted into a real image (visualized) by the intermediate image screen 36 .
The intermediate image screen 36 is not limited, and various known intermediate image screens that realize projected images in HUD projectors can be used.

Examples of the intermediate image screen 36 include a scattering film, a microlens array, and a screen for rear projection. When the intermediate image screen 36 is made of a plastic material, for example, if the intermediate image screen 36 has birefringence, the plane of polarization and the light intensity of the polarized light incident on the intermediate image screen 36 are disturbed, and as a result, colors appear in the projected image. Although unevenness or the like tends to occur, the problem of color unevenness can be reduced by using a retardation layer having a predetermined retardation.

The intermediate image screen 36 preferably has the function of spreading and transmitting incident projection light. This is because the projected image can be enlarged and displayed.
An example of such an intermediate image screen is an intermediate image screen composed of a microlens array. Microlens arrays used in HUDs are described, for example, in JP-A-2012-226303, JP-A-2010-145745, and JP-A-2007-523369.

Projected light that has been converted into a real image on the intermediate image screen 36 is reflected along a predetermined optical path by the mirror 38 and the concave mirror 40, passes through the transmission window 46 provided on the dashboard 42, and passes through the windshield. It is projected on the glass 10 and observed by the driver D (see the dashed line).

The mirror 38 is a known mirror used for adjusting the optical path of projection light in a projector. Also, the mirror 38 may be a so-called cold mirror that prevents the components of the projector 32 from being heated by sunlight incident through the windshield glass by reflecting visible light and transmitting infrared light.
On the other hand, the concave mirror 40 is a well-known concave mirror (concave mirror) used in a HUD projector that enlarges and projects projected light.

Although the illustrated projector 32 uses the mirror 38 and the concave mirror 40 as members for changing the optical path of projection light, the present invention is not limited to this.
For example, projector 32 may have only one of mirror 38 and concave mirror 40, or may include other light reflecting elements such as free-form mirrors in addition to or in place of mirror 38 and/or concave mirror 40. You may have one or more.
That is, the projector that constitutes the HUD of the present invention can use a configuration using various light reflecting elements.

The p-polarized projection light projected by the projector 32 and transmitted through the transmissive window 46 is transmitted through the first glass 12 and the intermediate film 16 and enters the polarization conversion layer 24 .
As described above, the polarization conversion layer 24 is a layer in which the helical orientation structure of the liquid crystal compound is fixed, and converts p-polarized light into circularly polarized light in the direction of rotation reflected by the cholesteric liquid crystal layer of the reflective layer 18 .
Of the circularly polarized projection light incident on the reflective layer 18, green light and blue light are reflected by the green-blue reflecting cholesteric liquid crystal layer 18GB, and red light is reflected by the red reflecting cholesteric liquid crystal layer 18R.
The circularly polarized projection light reflected by the reflective layer 18 reenters the polarization conversion layer 24 and is converted into p-polarized light by the polarization conversion layer 24 .
The projection light converted into p-polarized light by the polarization conversion layer 24 is applied to the observation position of the driver D. As shown in FIG. Here, since the projected image is p-polarized light, the projected image can be properly observed even when the driver D is wearing polarized sunglasses as described above.

On the other hand, when s-polarized light, such as reflected light from puddles and light reflected from the bonnet, is incident from outside the vehicle, this s-polarized light passes through the second glass 14, the heat seal layer 20, and the transparent base material 26. It is transmitted and enters the retardation layer 28 .
The glaring s-polarized light incident on the retardation layer 28 is converted into elliptically polarized light with a rotating direction corresponding to the s-polarized light due to the phase difference of the retardation layer 28 .
The elliptically polarized light that has passed through the retardation layer 28 is then incident on the reflective layer 18, that is, the cholesteric liquid crystal layer, is transmitted therethrough, and is converted into circularly polarized light in the rotating direction corresponding to the s-polarized light. This circularly polarized light is then converted into s-polarized light by passing through the polarization conversion layer 24 and passes through the windshield glass 10 .
That is, in the windshield glass 10 of the present invention, the glaring s-polarized light entering the windshield glass from outside the vehicle is transmitted as it is, so that it can be blocked by polarized sunglasses. Therefore, according to the windshield glass 10 of the present invention, in a HUD that projects p-polarized light, good suitability for polarized sunglasses against external light can be realized.

The windshield glass 10 of the present invention has a polarization conversion layer 24 in which the helically oriented structure of the liquid crystal compound is fixed, on the inside of the vehicle from the reflective layer 18, that is, the cholesteric liquid crystal layer.
Therefore, as will be described later in Examples, the retardation layer 28 is not provided, and s-polarized light that causes glare is incident from the outside of the vehicle, is transmitted through the reflective layer 18, that is, the cholesteric liquid crystal layer, and becomes external light containing a p-polarized component. Even so, the polarization conversion layer 24 can convert this p-polarized component back to s-polarized light.
Therefore, even if the windshield glass 10 of the present invention does not have the retardation layer 28, the s-polarized light that causes glare can be transmitted as it is. Aptitude for polarized sunglasses can be obtained.

Although the windshield glass and HUD of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements and modifications may be made without departing from the gist of the present invention. Good, of course.

EXAMPLES The present invention will be described more specifically below with reference to Examples of the present invention. Materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples, comparative examples, and preparation examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following Examples and Reference Examples.

[Example 1]
(Compositions 1 and 2 for forming a cholesteric liquid crystal layer)
Regarding the composition 1 for forming a cholesteric liquid crystal layer that forms a cholesteric liquid crystal layer with a selective reflection central wavelength of 550 nm and the composition 2 for forming a cholesteric liquid crystal layer that forms a cholesteric liquid crystal layer with a selective reflection central wavelength of 800 nm, the following were mixed to prepare a composition for forming a cholesteric liquid crystal layer having the following composition.
・Mixture 1: 100 parts by mass ・Fluorine-based horizontal alignment agent 1 (alignment control agent 1): 0.05 mass parts ・Fluorine-based horizontal alignment agent 2 (alignment control agent 2): 0.02 mass parts ・Right-rotating chiral agent LC756 (manufactured by BASF)
Adjust according to the target reflection wavelength Polymerization initiator IRGACURE OXE01 (manufactured by BASF)
1.0 parts by mass Solvent (methyl ethyl ketone) Amount that makes the solute concentration 20% by mass

Using the cholesteric liquid crystal layer-forming composition 1 and the cholesteric liquid crystal layer-forming composition 2, a single cholesteric liquid crystal layer having a thickness of 3 μm was formed on a temporary support in the same manner as in the production of the half mirror film described below. It was fabricated, and the reflection characteristics of visible light were confirmed.
As a result, all the produced cholesteric liquid crystal layers were right-handed circularly polarized light reflective layers, and the selective reflection center wavelength (center wavelength) of the cholesteric liquid crystal layer formed by the composition 1 for forming the cholesteric liquid crystal layer was 550 nm. The cholesteric liquid crystal layer of Composition 2 had a wavelength of 800 nm.

(Composition for forming polarization conversion layer)
The components below were mixed to prepare a composition for forming a polarization conversion layer having the following composition.
・Mixture 1: 100 parts by mass ・Fluorine-based horizontal alignment agent 1 (alignment control agent 1): 0.05 mass parts ・Fluorine-based horizontal alignment agent 2 (alignment control agent 2): 0.02 mass parts ・Right-handed chiral agent LC756 (manufactured by BASF)
Adjust according to the reflection wavelength that matches the target pitch number and film thickness ・Polymerization initiator IRGACURE OXE01 (manufactured by BASF)
1.0 parts by mass Solvent (methyl ethyl ketone) Amount that makes the solute concentration 20% by mass

A composition for forming a polarization conversion layer was prepared so that a cholesteric liquid crystal layer formed by adjusting the prescription amount of the right-handed chiral agent LC756 in the composition composition described above would have a desired selective reflection center wavelength λ. bottom. The selective reflection center wavelength λ was determined by FTIR (Spectrum Two, manufactured by Perkin Elmer) after forming a single cholesteric liquid crystal layer having a thickness of 3 μm on a temporary support.
The film thickness d of the helical orientation structure can be represented by "the pitch P of the helical orientation structure×the number of pitches". As described above, the pitch P of the helical alignment structure is the length of 1 pitch in the helical alignment structure, and 1 pitch means that the helically aligned liquid crystal compound rotates 360°. In addition, in the cholesteric liquid layer, the selective reflection center wavelength λ coincides with "one pitch length P×in-plane average refractive index n" (λ=P×n). Therefore, the pitch P is "selective reflection center wavelength λ/in-plane average refractive index n" (P=λ/n).
Accordingly, the composition for forming the polarization conversion layer was prepared so that the selective reflection central wavelength λ was 8580 nm when the cholesteric liquid crystal layer was formed.

(Preparation of half mirror film)
A polyethylene terephthalate film (Cosmoshine A4100, manufactured by Toyobo Co., Ltd.) having a thickness of 100 μm was prepared as a temporary support.
One surface of the temporary support was rubbed (rayon cloth, pressure: 0.1 kgf (0.98 N), rotation speed: 1000 rpm (revolutions per minute), transport speed: 10 m/min, number of reciprocations: 1 reciprocation).

Cholesteric liquid crystal layer-forming composition 1 was applied to the rubbing-treated surface of the temporary support using a wire bar at room temperature so that the thickness of the dry film after drying was 0.8 μm to obtain a coating layer. rice field.
After drying the coating layer at room temperature for 30 seconds, it was heated in an atmosphere of 85° C. for 2 minutes. After that, in an environment with an oxygen concentration of 1000 ppm or less, ultraviolet light is irradiated at 60° C. with a D bulb (90 mW/cm ² lamp) manufactured by Fusion Co., Ltd. for 6 to 12 seconds at an output of 60% to fix the cholesteric liquid crystal phase. , a cholesteric liquid crystal layer having a thickness of 0.8 μm was obtained. This cholesteric liquid crystal layer is a red-reflecting cholesteric liquid crystal layer that selectively reflects red light.
Next, on the surface of the obtained cholesteric liquid crystal layer, a layer of the cholesteric liquid crystal layer forming composition 2 having a thickness of 0.55 μm was laminated by repeating the same steps using the cholesteric liquid crystal layer forming composition 2. . This cholesteric liquid crystal layer is a green reflecting cholesteric liquid crystal layer that selectively reflects green light.

Next, a composition for forming a polarization conversion layer was applied to the surface of the formed cholesteric liquid crystal layer so as to have a film thickness of 2.2 μm to form a polarization conversion layer.
The polarization conversion layer was formed in the same manner as the cholesteric liquid crystal layer described above.
The pitch number of the formed polarization conversion layer was 0.4.
As described above, this polarization conversion layer has a selective reflection central wavelength (reflection central wavelength) of 8580 nm when used as a cholesteric liquid crystal layer. The refractive index of the polarization conversion layer, which is a liquid crystal layer, is about 1.56. Therefore, "(1560xy)/x" substantially matches the selective reflection center wavelength.

Thus, a half-mirror film with a temporary support having a reflective layer comprising two cholesteric liquid crystal layers and a polarization conversion layer was obtained.
When the reflection spectrum of the half mirror film with a temporary support was measured with a spectrophotometer (manufactured by JASCO Corporation, V-670), a reflection spectrum having a selective reflection center wavelength (center wavelength) at a wavelength of 550 nm and a wavelength of 800 nm was obtained. was taken.

(Production of windshield glass>
A glass plate (FL2, 300×300 mm, thickness 2 mm, manufactured by Central Glass Co., Ltd.) was prepared. This glass plate was bent to form a curved glass having a radius of curvature of 1500 mm, which was used as the first glass.
A 0.38 mm thick PVB film manufactured by Sekisui Chemical Co., Ltd. cut into the same size was laminated as an intermediate film on the convex side of the first glass.
A half mirror film with a temporary support cut into the same size was laminated on the intermediate film with the polarization conversion layer facing the intermediate film. Then, the temporary support was peeled off from the half mirror film.
A glass plate (FL2, manufactured by Central Glass Co., Ltd., visible light transmittance of 90%) of 300 mm long×300 mm wide and 2 mm thick was laminated on the half mirror film.
After holding this laminate at 90° C. and 10 kPa (0.1 atmosphere) for one hour, it was heated in an autoclave (manufactured by Kurihara Seisakusho) at 115° C. and 1.3 MPa (13 atmospheres) for 20 minutes to remove air bubbles. , windshield glass was produced.
This windshield glass has a layer structure of "second glass/reflective layer/polarization conversion layer/intermediate film/first glass".

[Example 2]
(Composition for forming retardation layer)
The following components were mixed to prepare a composition for forming a retardation layer having the following composition.
・Mixture 1 100 parts by mass ・Fluorine-based horizontal alignment agent 1 (alignment control agent 1) 0.05 mass parts ・Fluorine-based horizontal alignment agent 2 (alignment control agent 2) 0.01 mass parts ・Polymerization initiator IRGACURE OXE01 (BASF company)
1.0 parts by mass Solvent (methyl ethyl ketone) Amount that makes the solute concentration 20% by mass

(Preparation of half mirror film)
A temporary support similar to that of Example 1 was prepared and subjected to rubbing treatment in the same manner as in Example 1.
As conceptually shown in FIG. 3, the rubbing treatment is performed so that the angle α between the rubbing direction Sa and the long side direction H is 35° clockwise with the long side direction H of the temporary support S as a reference. gone.

The composition for forming a retardation layer was applied to the rubbing-treated surface of the temporary support using a wire bar, and then dried.
Then, it is placed on a hot plate at 50° C., and irradiated with ultraviolet rays for 6 seconds in an environment with an oxygen concentration of 1000 ppm or less, using an electrodeless lamp “D bulb” (60 mW/cm ² ) manufactured by Fusion UV Systems Co., Ltd. to transform the liquid crystal phase. Fixed. As a result, a desired front retardation, that is, a retardation layer having a thickness adjusted to obtain a desired front retardation was obtained.
When the retardation of the formed retardation layer was measured by AxoScan, it was 110 nm.

A cholesteric liquid crystal layer and a polarization conversion layer are formed on the surface of the retardation layer in the same manner as in Example 1 to provide a temporary support having a retardation layer, a reflective layer comprising two cholesteric liquid crystal layers, and a polarization conversion layer. A body-attached half-mirror film was obtained.

(Production of windshield glass)
A windshield glass was produced in the same manner as in Example 1 using this half-mirror film with a temporary support. In addition, the windshield glass was regarded as the vertical direction with the long side direction H as the vertical direction.
This windshield glass has a layer structure of "second glass/retardation layer/reflective layer/polarization conversion layer/intermediate film/first glass".

[Example 3]
In the preparation of the composition for forming the polarization conversion layer, the prescription amount of the right-handed chiral agent LC756 was adjusted so that the selective reflection central wavelength (reflection central wavelength) in the cholesteric liquid crystal layer was 7800 nm.
A half mirror film with a temporary support was produced in the same manner as in Example 2, except that this composition for forming a polarization conversion layer was used and the film thickness of the polarization conversion layer was changed to 1.1 μm. The pitch number of the polarization conversion layer was 0.22.
A windshield glass was produced in the same manner as in Example 1 using this half-mirror film with a temporary support.
This windshield glass has a layer structure of "second glass/retardation layer/reflective layer/polarization conversion layer/intermediate film/first glass".

[Example 4]
(Saponification of cellulose acylate film)
A 40 μm-thick cellulose acylate film (TAC) was produced by the same production method as in Example 20 of WO 2014/112575. UV-531 manufactured by Teisei Kako Co., Ltd. was added to this cellulose acylate film as an ultraviolet absorber. The amount added was 3 phr (per hundred resin).
The produced cellulose acylate film was passed through a dielectric heating roll at a temperature of 60°C to raise the film surface temperature to 40°C. After that, an alkaline solution having the composition shown below was applied to one side of the film using a bar coater at a coating amount of 14 mL/m ² and heated to 110°C under a steam type far-infrared heater (manufactured by Noritake Co., Ltd.). was held for 10 seconds.
Then, using the same bar coater, 3 mL/m ² of pure water was applied.
Next, after repeating water washing with a fountain coater and draining with an air knife three times, the film was dried by staying in a drying zone at 70° C. for 5 seconds to prepare a saponified cellulose acylate film.
When the in-plane retardation of the saponified cellulose acylate film was measured by AxoScan, it was 1 nm.

(Composition of alkaline solution)
・Potassium hydroxide 4.7 parts by mass ・Water 15.7 _{parts by mass ・Isopropanol 64.8 parts by mass ・Surfactant (C16H33O(CH2CH2O)10H ) 1.0 parts by} mass ・Propylene Glycol 14.9 parts by mass

<Formation of Alignment Film>
On the saponified surface of the saponified cellulose acylate film, 24 mL/m ² of a composition for forming an alignment film having the composition shown below was applied with a wire bar coater and dried with hot air at 100° C. for 120 seconds.

(Coating liquid for forming alignment film)
· Modified polyvinyl alcohol shown below 28 parts by mass · Citric acid ester (AS3, manufactured by Sankyo Chemical Co., Ltd.) 1.2 parts by mass · Photoinitiator (Irgacure 2959, manufactured by BASF) 0.84 parts by mass · Glutaraldehyde 2.8 Parts by mass Water 699 parts by mass Methanol 226 parts by mass

(denatured polyvinyl alcohol)

(Preparation of half mirror film)
A cellulose acylate film having an orientation film thus prepared was used as a transparent substrate.
A half-mirror film was produced in the same manner as in Example 2 using a transparent base material on which an orientation film was formed instead of the polyethylene terephthalate film used as the temporary support. The rubbing treatment was applied to the alignment film.
That is, this half-mirror film is a half-mirror film with a transparent substrate, which has a retardation layer, a reflective layer having two cholesteric liquid crystal layers, and a polarization conversion layer.

A windshield glass was produced in the same manner as in Example 1 using this half mirror film with a transparent substrate. However, in this example, the transparent substrate was not peeled off.
This windshield glass has a layer structure of "second glass/transparent substrate/retardation layer/reflective layer/polarization conversion layer/intermediate film/first glass".

[Example 5]
In order to form a heat seal layer, the following ingredients were mixed to prepare a heat seal layer forming coating liquid.

<Coating solution for forming heat seal layer>
PVB sheet piece (manufactured by Sekisui Chemical Co., Ltd., S-lec film) 5.0 parts by mass Methanol 90.25 parts by mass Butanol 4.75 parts by mass <Formation of heat seal layer>
A half mirror film with a transparent substrate was produced in the same manner as in Example 4.
The coating solution for forming a heat seal layer was applied to the transparent substrate of this half mirror film using a wire bar, dried, and heat-treated at 50° C. for 1 minute to form a heat seal layer having a thickness of 1 μm. .

A windshield glass was produced in the same manner as in Example 1, except that this half mirror film with a transparent substrate having a heat seal layer was used.
This windshield glass has a layer structure of "second glass/heat seal layer/transparent substrate/retardation layer/reflective layer/polarization conversion layer/intermediate film/first glass".

[Comparative Example 1]
(Preparation of half mirror film)
A transparent substrate similar to that of Example 4 was prepared and rubbed. However, as conceptually shown in FIG. 3, the rubbing process was performed so that the angle α between the rubbing direction Sa and the long side direction H was 50° clockwise.
On the rubbing-treated surface of this transparent substrate, a retardation layer and a reflective layer were formed in the same manner as in Example 2 to produce a half mirror film with a transparent substrate. However, the thickness of the retardation layer was adjusted so that the front retardation was 142 nm.

(Production of windshield glass)
A heat seal layer was formed in the same manner as in Example 5 on the transparent base material of the half mirror film with the transparent base material.
On the surface of the same first glass as in Example 1, a half mirror film with a transparent substrate was laminated with the heat seal layer facing.
An intermediate film similar to that of Example 1 was laminated on the reflective layer of the half mirror film, and a second glass similar to that of Example 1 was laminated on the intermediate film.
A windshield glass was produced in the same manner as in Example 1 using this laminate.
This windshield glass has a layer structure of "second glass/intermediate film/reflective layer/retardation layer/transparent substrate/heat seal layer/first glass".

[Comparative Example 2]
A half mirror film with a transparent substrate was produced in the same manner as in Comparative Example 1, except that the retardation layer was not provided.
A windshield glass was produced in the same manner as in Comparative Example 1 using this half mirror film.
This windshield glass has a layer structure of "second glass/intermediate film/reflective layer/transparent substrate/heat seal layer/first glass".

[Comparative Example 3]
(Preparation of half mirror film)
A transparent substrate similar to that of Example 4 was prepared and rubbed. However, as conceptually shown in FIG. 3, the rubbing process was performed so that the angle α between the rubbing direction Sa and the long side direction H was −50° clockwise.
A retardation layer and a reflective layer were formed on the rubbing-treated surface of this transparent substrate in the same manner as in Example 2 to prepare a half mirror film with a transparent substrate. However, the thickness of the retardation layer was adjusted so that the front retardation was 310 nm.

(Production of windshield glass)
An intermediate film similar to that of Example 1 was laminated on the first glass similar to that of Example 1.
A half mirror film with a transparent substrate was laminated on the intermediate film with the transparent substrate facing the intermediate film.
A heat seal layer was formed on the reflective layer of the half mirror film with a transparent substrate in the same manner as in Example 5, and the second glass as in Example 1 was laminated thereon.
A windshield glass was produced in the same manner as in Example 1 using this laminate.
This windshield glass has a layer structure of "second glass/heat seal layer/reflective layer/retardation layer/transparent substrate/intermediate film/first glass".

[Comparative Examples 4 to 6]
In the preparation of the composition for forming the polarization conversion layer, by adjusting the prescription amount of the right-handed chiral agent LC756, the selective reflection central wavelength (reflection central wavelength) in forming the cholesteric liquid crystal layer was adjusted.
Examples except that this composition for forming a polarization conversion layer was used and the film thickness of the polarization conversion layer was changed to 3.5 μm (Comparative Example 4) or 1.1 μm (Comparative Examples 5 and 6). A half mirror film with a transparent support having a heat seal layer was prepared in the same manner as in 5. The pitch numbers of the polarization conversion layers were 0.8 (Comparative Example 4), 0.6864 (Comparative Example 5), and 0.0858 (Comparative Example 6).
A windshield glass was produced in the same manner as in Example 1 using this half-mirror film with a temporary support.
These windshield glasses have a layer structure of "second glass/heat seal layer/transparent substrate/retardation layer/reflective layer/polarization conversion layer/intermediate film/first glass".

[evaluation]
The prepared windshield glass was evaluated for its suitability for polarized sunglasses against external light, light resistance, impact resistance, and p-polarized reflectance.

(Polarized sunglasses suitability for external light (polarized sunglasses suitability))
S-polarized light is incident from the second glass side at 65° to the normal direction of the glass, and p-polarized light transmitted from the first glass side is transmitted by a spectrophotometer (manufactured by JASCO Corporation, V-670). The index spectrum was measured.
At this time, a linear polarizing plate was placed in the light receiving portion of the spectrophotometer so that the vertical direction of the windshield glass and the transmission axis of the p-polarized light incident on the spectrophotometer were parallel.
According to JIS R3106, at wavelengths between 380 and 780 nm in increments of 10 nm, the visible light transmittance was calculated by multiplying the coefficient corresponding to the visual sensitivity and the emission spectrum of the D65 light source, and evaluated as the suitability of polarized sunglasses for external light. Evaluation was performed according to the following evaluation criteria.
A+ Less than 2% A 2% or more and less than 3% B 3% or more and less than 5% C 5% or more

(light resistance)
The produced windshield glass was cut into 50 mm×50 mm.
The cut windshield glass was subjected to a light resistance test based on JIS R 3212 using a super xenon weather meter (manufactured by Suga Test Instruments Co., Ltd.) (temperature inside the device: 45°C, distance between light source and sample: 230 mm, UV irradiation amount 750 W). was performed for 1000 hours. Evaluation was performed according to the following evaluation criteria.
A Decrease in transmittance is less than 2% (no change in reflected color)
B Decrease in transmittance is 2% or more (reflected color is yellower than that without light resistance)

(shock resistance)
A falling ball test was performed on the produced windshield glass based on JIS R 3212.
Specifically, a steel ball (227 g, diameter 38 mm) was dropped from a height of 9 m onto the windshield glass cooled at −20° C., and the amount of the dropped glass was measured. Evaluation was performed according to the following evaluation criteria.
A Dropped amount of glass is less than 10g B Dropped amount of glass is 10g or more and less than 15g C Dropped amount of glass is 15g or more

(p-polarized reflectance)
From the first glass side, p-polarized light was incident from the direction of 65° with respect to the normal direction of the glass, and the reflectance spectrum of the specularly reflected light was measured with a spectrophotometer (manufactured by JASCO Corporation, V-670). Specularly reflected light is light in the direction opposite to the incident direction with respect to the normal direction within the incident surface, and in the direction at 65° with respect to the normal direction.
At this time, the vertical direction of the windshield glass was made parallel to the transmission axis of p-polarized light incident on the spectrophotometer.
In accordance with JIS R3106, the reflectance was multiplied by the coefficient corresponding to the visibility and the emission spectrum of the D65 light source at wavelengths of 380 to 780 nm in increments of 10 nm to calculate the projected image reflectance, which was evaluated as luminance. Evaluation was performed according to the following evaluation criteria.
A 25% or more (The image can be seen well with the p-polarized reflection system of the HUD.)
B 20% or more and less than 25% (Image is visible in the HUD's p-polarized reflection system.)
Results are shown in Table 1 below.

As shown in Examples 1 to 5 in Table 1, the windshield glass of the present invention has good suitability for polarized sunglasses against external light, and also has a high p-polarized reflectance. That is, according to the HUD of the present invention using the windshield glass of the present invention, even when the driver wears polarized sunglasses, the projected image of the HUD can be observed, and glare incident from outside the vehicle becomes s Polarized light can be sufficiently blocked by polarized sunglasses.
On the other hand, in Comparative Examples 1 to 3 having no polarization conversion layer as well as Comparative Example 4 in which the thickness y of the polarization conversion layer exceeds 3 μm even with the polarization conversion layer, (1560*y)/x] is less than 3000, and Comparative Example 6, where the pitch number x of the polarization conversion layer is less than 0.1, are not suitable for sunglasses.
Incidentally, as shown in Example 1 and Comparative Example 2, the polarization conversion layer in which the helical alignment structure of the liquid crystal compound is fixed is equivalent to the retardation layer conventionally used in a HUD that irradiates p-polarized projection light. P-polarized light can be circularly polarized with performance.
Further, as shown in Example 1 and Comparative Examples 1 and 3, according to the windshield glass of the present invention, the p-polarized light is converted into circularly polarized light by the polarization conversion layer in which the helically oriented structure of the liquid crystal compound is fixed. As compared with Comparative Example 1, which is a conventional windshield glass in which p-polarized light is converted into circularly polarized light by a retardation layer, excellent suitability for polarized sunglasses against external light can be obtained.

As shown in Examples 1 to 5 and Comparative Examples 1 and 2, excellent impact resistance can be obtained by providing the intermediate film adjacent to the first glass on the vehicle interior side.
As shown in Example 2, by providing a retardation layer between the reflective layer (cholesteric liquid crystal layer) and the second glass on the outside of the vehicle, it is possible to obtain better suitability for sunglasses against external light.
As shown in Example 3, the pitch number x of the polarization conversion layer is set in the range of 0.2 to 0.8, the film thickness y is set in the range of 0.6 to 2.0 μm, and (1560*y)/x is in the range of 6,000 to 10,000, it is also possible to obtain better suitability for sunglasses against external light.
Furthermore, as shown in Examples 4 and 5, excellent light resistance can be obtained by providing a transparent substrate and adding an ultraviolet absorber to the transparent substrate.
From the above results, the effect of the present invention is clear.

It can be suitably used for an in-vehicle HUD or the like.

10 windshield glass 12 first glass 14 second glass 16 intermediate film 18 reflective layer 18GB green blue reflecting cholesteric liquid crystal layer 18R red reflecting cholesteric liquid crystal layer 20 heat seal layer 24 polarization conversion layer 26 transparent substrate 28 retardation layer 30 HUD ( head-up display system)
32 projector 34 image forming unit 36 intermediate image screen 38 mirror 40 concave mirror 42 dashboard 46 transmission window 50 LCD (liquid crystal display)
52 Projection lens D Driver

Claims (9)

a first curved glass;
a polarization conversion layer in which a helically oriented structure of a liquid crystal compound is fixed;
a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase;
a second curved glass having a concave surface facing the first curved glass;
The polarization conversion layer, the cholesteric liquid crystal layer and the second curved glass are provided in this order on the convex side of the first curved glass,
The windshield glass, wherein the pitch number x of the helical orientation structure in the polarization conversion layer and the film thickness y (unit: μm) of the polarization conversion layer satisfy all of the following formulas (a) to (c).
(a) 0.1≤x≤1.0
(b) 0.5≤y≤3.0
(c) 3000≦(1560*y)/x≦50000 having a retardation layer between the cholesteric liquid crystal layer and the second curved glass;
The retardation layer has a front retardation of 50 to 140 nm at a wavelength of 550 nm, and the direction corresponding to the vertical direction above the surface of the first curved glass when the windshield glass is mounted on the vehicle is 0 °. The windshield glass according to claim 1, wherein the angle of the slow axis is ±10 to 50°. 3. The windshield glass according to claim 1, wherein said pitch number x and said film thickness y (unit: μm) satisfy all of the following formulas (d) to (f).
(d) 0.2≤x≤0.8
(e) 0.6≤y≤2.0
(f) 6000≦(1560*y)/x≦10000 The windshield glass according to any one of claims 1 to 3 , comprising a transparent substrate between the cholesteric liquid crystal layer and the second curved glass. A windshield glass according to claim 4 , wherein the transparent substrate comprises an ultraviolet absorber. The windshield glass according to any one of claims 1 to 5 , further comprising an intermediate film between said first curved glass and said polarization conversion layer. The windshield glass according to any one of claims 1 to 6 , having a heat seal layer between the cholesteric liquid crystal layer and the second curved glass. A windshield glass according to any one of claims 1 to 7 ;
A head-up display system comprising a projector that irradiates a concave surface of the first curved glass of the windshield glass with projection light. 9. The head-up display system of claim 8 , wherein the projector emits p-polarized projection light.

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