JP6988353B2 - Reflectors, display devices and mobiles - Google Patents

Description

The present invention relates to a reflector, a display device having a reflector, and a moving body having the display device.

Many moving objects such as cars, ships, railroad cars, and airplanes are equipped with display devices. Patent Document 1 discloses, for example, a head-up display as a display device mounted on a moving body. In the display device disclosed in Patent Document 1, the image forming device that emits image light is arranged at a position that is not directly visible, such as inside a dashboard. Then, the image light formed by the image forming apparatus is guided to a position visible to the driver by a guiding means such as a mirror.

JP-A-2015-155948

By the way, the use of a cholesteric liquid crystal structure layer as a guiding means for guiding the above-mentioned image light has been studied. The cholesteric liquid crystal structure layer has wavelength selectivity in addition to circularly polarized light selectivity, and can selectively guide light in a specific wavelength range having a specific circularly polarized light component, so that image light is selectively selected. It is considered to be useful for guiding to. In particular, in a full-color display device, a plurality of cholesteric liquid crystal structure layers having different wavelength ranges (for example, wavelength ranges of red (R), green (G), and blue (B), which are the three primary colors of light) as selective reflection wavelength ranges. It is being studied to use a laminated body obtained by laminating the above as a polarization selective reflection layer for guiding image light. In this case, the image light is obliquely incident on the polarization selective reflection layer and guided to a projection surface such as a windshield.

However, when the image light is obliquely incident on the polarization selective reflection layer, the following problems have been found. That is, when the image light is obliquely incident on the polarization selective reflection layer formed by laminating a plurality of cholesteric liquid crystal structural layers, the image light may not be reflected as desired and a desired color display may not be obtained. .. Such a problem becomes more remarkable as the angle of incidence of the image light on the polarization selective reflection layer is larger.

The present invention has been made in consideration of the above points, and is a display device provided with a polarization selective reflection layer in which a plurality of cholesteric liquid crystal structural layers are laminated, and image light is obliquely applied to the polarization selective reflection layer. It is an object of the present invention to provide a display device capable of obtaining a display of a desired color even when incident. It is also an object of the present invention to provide a mobile body having such a display device and a reflector including a plurality of cholesteric liquid crystal structural layers.

The display device according to the present invention is
An image forming device that emits image light and
A polarization selective reflection layer that reflects the image light and changes the optical path of the image light is provided.
The polarization selective reflection layer includes a plurality of cholesteric liquid crystal structure layers and a compensating layer having in-plane birefringence arranged between two cholesteric liquid crystal structure layers included in the plurality of cholesteric liquid crystal structure layers. ..

In the display device according to the present invention, the compensation layer having in-plane birefringence may be arranged between any two adjacent cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers.

Further, in the display device according to the present invention, the compensation layer may have a positive A plate characteristic or a negative A plate characteristic.

Further, the display device according to the present invention may further include a 1/4 wavelength retardation layer arranged at a position on the optical path of the image light from the image forming device to the polarization selective reflection layer. In this case, the display device according to the present invention may further include a 1/4 wavelength retardation layer arranged at a position on the optical path of the image light reflected by the polarization selective reflection layer.

Alternatively, the display device according to the present invention is arranged at a position on the optical path of the image light from the image forming apparatus to the polarization selective reflection layer and on the optical path of the image light reflected by the polarization selective reflection layer. A 1/4 wavelength retardation layer may be further provided. In this case, in the display device according to the present invention, the 1/4 wavelength retardation layer may be laminated on the polarization selective reflection layer.

Further, the display device according to the present invention may further include a polarizing element arranged on the optical path of the image light after being reflected by the polarization selective reflection layer and transmitted through the 1/4 wavelength retardation layer. ..

Further, in the display device according to the present invention, the image forming device may emit the image light composed of the light of one of the linearly polarized light components.

Further, the image forming apparatus may include a liquid crystal display apparatus.

Further, in the display device according to the present invention, the polarization selective reflection layer includes a cholesteric liquid crystal structure layer that selectively reflects light of a right circularly polarized light component and a cholesteric liquid crystal structure layer that selectively reflects light of a left circularly polarized light component. You may be. In this case, the display device according to the present invention may further include a polarizing element arranged on the optical path of the image light after being reflected by the polarization selective reflection layer.

Further, in the display device according to the present invention, in the image forming apparatus, the light source, the digital micromirror device that changes the optical path of the light from the light source, and the light whose optical path is changed by the digital micromirror device are incident. It may include a screen and.

Further, in the display device according to the present invention, the image forming apparatus includes a laser light source that emits a laser beam, a scanning device that changes the optical path of the laser beam over time, and the laser whose optical path is adjusted by the scanning device. It may include a screen on which light is incident.

The mobile body according to the present invention includes any of the above-mentioned display devices according to the present invention.

The reflector according to the present invention includes a plurality of cholesteric liquid crystal structural layers and a compensating layer having in-plane birefringence arranged between the two cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers. ..

Further, in the reflector according to the present invention, even if the compensating layer having in-plane birefringence is arranged between any two adjacent cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers. good.

Further, in the reflector according to the present invention, the compensation layer may have a positive A plate characteristic or a negative A plate characteristic.

Further, the reflector according to the present invention may have a 1/4 wavelength retardation layer laminated.

Further, the reflector according to the present invention may include a cholesteric liquid crystal structure layer that selectively reflects the light of the right circularly polarized light component and a cholesteric liquid crystal structure layer that selectively reflects the light of the left circularly polarized light component.

According to the present invention, it is a display device provided with a polarization selective reflection layer in which a plurality of cholesteric liquid crystal structural layers are laminated, and a desired color display can be obtained even if image light is obliquely incident on the polarization selective reflection layer. It is possible to provide a display device capable of providing a display device. It is also possible to provide a mobile body having such a display device and a reflector including a plurality of cholesteric liquid crystal structural layers.

FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a vertical sectional view schematically showing a moving body and a display device. FIG. 2 is a diagram showing a selective reflector and an image forming apparatus that may be included in the display device of FIG. FIG. 3 is a diagram showing a modification of a polarization selective reflection layer that can be included in the selective reflector. FIG. 4 is a diagram showing an example of a laminated body having a compensation layer between a plurality of cholesteric liquid crystal structure layers. FIG. 5 is a diagram showing an example of a laminated body having no compensation layer between a plurality of cholesteric liquid crystal structural layers. FIG. 6 is a graph showing the reflection characteristics of the laminate shown in FIGS. 4 and 5. FIG. 7 is a diagram showing another example of a laminated body having a compensation layer between a plurality of cholesteric liquid crystal structure layers. FIG. 8 is a diagram showing another example of a laminated body having no compensation layer between a plurality of cholesteric liquid crystal structural layers. FIG. 9 is a graph showing the reflection characteristics of the laminate shown in FIGS. 7 and 8. FIG. 10 is a vertical sectional view showing a modified example of the display device. FIG. 11 is a vertical sectional view showing another modification of the display device. FIG. 12 is a vertical sectional view showing still another modification of the display device. FIG. 13 is a diagram for explaining a modification of the image forming apparatus. FIG. 14 is a diagram for explaining another modification of the image forming apparatus. FIG. 15 is a vertical sectional view showing still another modification of the display device. FIG. 16 is a diagram showing a selective reflector that may be included in the display device of FIG. FIG. 17 is a diagram showing a modified example of the polarization selective reflection layer that can be included in the selective reflection plate shown in FIG. FIG. 18 is a vertical sectional view showing still another modification of the display device.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, the scale and the aspect ratios are appropriately changed and exaggerated from those of the actual product for the convenience of illustration and comprehension.

1 to 3 are diagrams for explaining one embodiment according to the present invention. Of these, FIG. 1 is a vertical sectional view showing the entire configuration of the display device together with a part of the moving body, and FIG. 2 is a vertical sectional view showing a main part of the display device. FIG. 3 is a vertical sectional view showing a modification of a polarization selective reflection layer that may be included in a display device.

As shown in FIG. 1, the moving body 1 has a moving body main body 2 and a display device 10 mounted on the moving body main body 2. As the moving body main body 2, a car, a ship, a railroad vehicle, an airplane, or the like can be exemplified. In the example shown in FIG. 1, the mobile body 2 is an automobile. In this example, the display device 10 is arranged in the dashboard 4 and projects an image on the windshield 3. The image light projected toward the windshield 3 is reflected by the windshield 3 so that it can be observed by the driver of the moving body main body 2. The driver so as to visually recognize the virtual image at a position in front of the windshield 3 by the distance corresponding to the optical path length of the image light Li from the image forming device 30 included in the display device 10 to the windshield 3. Become. That is, in the example shown in FIG. 1, the display device 10 is configured as a projection type display device, more specifically, a head-up display.

In the example shown in FIG. 1, the dashboard 4 is formed with an opening 4a. The image light Li from the display device 10 goes to the windshield 3 through the opening 4a. On the other hand, as shown in FIG. 1, the external light Lx, particularly sunlight, incident on the inside of the moving body main body 2 through the windshield 3 travels in the opposite direction in the optical path of the image light Li and is inside the display device 10. Incident to. The image forming apparatus 30 included in the display apparatus 10 includes optical films having particularly low heat resistance, and its function may be impaired by receiving external light Lx. In one embodiment described below, a device is made to effectively suppress the heating of the image forming apparatus 30 included in the display device 10. Hereinafter, the details of the display device 10 in the present embodiment will be described.

Not limited to automobiles, the moving body 1 is usually provided with a display device 10, and the driver or the operator of the moving body 1 is in a state of the moving body main body 2 via the display device 10. And the surroundings of the mobile body 2 can be confirmed. The driver or operator of the mobile body 1 is usually located in an area partitioned by transparent glass or the like, and grasps the external situation through the transparent glass. Therefore, the display device 10 mounted on the mobile body 2 tends to be installed in an environment in which external light Lx, particularly sunlight, is easily received. The embodiment described below is not limited to the automobile, but is widely useful in the display device 10 generally mounted on the mobile body 1.

As shown in FIG. 1, the display device 10 guides the housing 20, the image forming device 30 arranged in the housing 20, and the image light Li formed by the image forming device 30 to the outside of the housing 20. It has a guiding means 55 and the like. The guiding means 55 includes a selective reflector (reflector) 60, and the selective reflector 60 has a polarized selective reflective layer 70 including a plurality of cholesteric liquid crystal structural layers. Further, in the illustrated example, the image light Li from the image forming apparatus 30 is composed of the light of one of the linearly polarized light components. Corresponding to such an image forming apparatus 30, a 1/4 wavelength retardation layer 50 is provided between the image forming apparatus 30 and the guiding means 55. Hereinafter, each component will be described.

The housing 20 is made of resin or metal. As shown in FIG. 1, the housing 20 is formed with an opening 21 at a position facing the windshield 3. The opening 21 is provided with a transparent cover 25 having visible light transmission. As a specific example, the transparent cover 25 can be a transparent plate made of a polycarbonate resin or an acrylic resin. Further, the transparent cover 25 is an infrared ray (a concept including near infrared rays) within a range that does not impair the transmission of the image light Li of the image forming apparatus 30 which is visible light for the purpose of suppressing the incident of infrared rays into the housing 20. It may function as an infrared reflecting film that reflects infrared rays or an infrared absorbing film that absorbs infrared rays.

The image forming apparatus 30 is an apparatus for forming an image, and emits image light Li that forms an image. In the example shown in FIGS. 1 and 2, the image light Li is composed of visible light in a plurality of wavelength ranges. As shown in FIG. 2, a liquid crystal display device 31 can be used as the image forming device 30.

The liquid crystal display device 31 includes a liquid crystal display panel 32 and a surface light source device 33 arranged on the back side of the liquid crystal display panel 32 and illuminating the liquid crystal display panel 32 in a plane shape from the back side. The surface light source device 33 may be configured by various types of backlights such as a direct type and an edge light type. The liquid crystal display panel 32 functions as a shutter that controls the transmission or blocking of light from the surface light source device 33 for each pixel, and can display an image on the display surface.

The illustrated liquid crystal display panel 32 has a lower polarizing plate 32a, a liquid crystal cell 32b, and an upper polarizing plate 32c in order from the side of the surface light source device 33. The lower polarizing plate 32a and the upper polarizing plate 32c are absorption-type polarizing elements, and decompose the incident light into two orthogonal polarizing components (P wave and S wave) in one direction (direction parallel to the transmission axis). ), And absorbs the linearly polarized light component (for example, S wave) that vibrates in the other direction (direction parallel to the absorption axis) orthogonal to the one direction. It has a function.

An electric field can be applied to the liquid crystal cell 32b for each region forming one pixel. Then, the orientation direction of the liquid crystal molecules in the liquid crystal cell 32b changes depending on the presence or absence of the electric field application. As an example, the polarization component in a specific direction transmitted through the lower polarizing plate 32a arranged on the light entrance side rotates its polarization direction by 90 ° when passing through the liquid crystal cell 32b to which no electric field is applied, while rotating the polarization direction by 90 °. The polarization direction is maintained as it passes through the liquid crystal cell 32b to which an electric field is applied. In this case, whether the polarizing component vibrating in a specific direction transmitted through the lower polarizing plate 32a further transmits the upper polarizing plate 32c arranged on the light emitting side of the lower polarizing plate 32a depending on the presence or absence of an electric field applied to the liquid crystal cell 32b. Alternatively, it can be controlled whether it is absorbed by the upper polarizing plate 32c and blocked.

In this way, the liquid crystal display panel 32 (liquid crystal display unit) can control the transmission or blocking of light from the surface light source device 33 for each pixel. The details of the liquid crystal display device 31 are described in various publicly known documents (for example, "Flat Panel Display Encyclopedia (supervised by Tatsuo Uchida and Hiraki Uchiike)" published by Kogyo Chosakai in 2001). The above detailed description will be omitted.

The image light Li emitted from the liquid crystal display device 31 is the light of one of the linearly polarized light components corresponding to the transmission axis of the upper polarizing plate 32c. Then, in the illustrated example, the image light Li emitted from the image forming apparatus 30 is incident on the 1/4 wavelength retardation layer 50. The 1/4 wavelength retardation layer 50 imparts a phase difference of 1/4 wavelength to the transmitted light. The image light Li composed of the light of one linearly polarized light component is converted into a right circularly polarized light component or a left circularly polarized light component by passing through the 1/4 wavelength retardation layer 50. The orientation of the slow axis of the 1/4 wavelength retardation layer 50 is adjusted so that the image light Li transmitted through the 1/4 wavelength retardation layer 50 is converted into a right circularly polarized light component or a left circularly polarized light component. And are arranged. In the examples shown in FIGS. 1 and 2, the image light Li transmitted through the 1/4 wavelength retardation layer 50 is converted into a right circularly polarized light component. Note that, in FIGS. 1 and 2, the 1/4 wavelength retardation layer 50 is arranged apart from the image forming apparatus 30, but is not limited to this. The 1/4 wavelength retardation layer 50 may be fixed to the image forming apparatus 30. For example, the 1/4 wavelength retardation layer 50 may be laminated on the image forming surface of the image forming apparatus 30. Further, it may be laminated on the light input surface 70a of the polarization selective reflection layer 70 described later.

Next, the guiding means (optical path adjusting optical system) 55 will be described. The guiding means 55 guides the image light Li from the image forming apparatus 30 toward the windshield 3. That is, the guiding means 55 is a projection optical system (projection optical system) that projects the image light Li from the image forming apparatus 30 onto the front glass 3. The guiding means 55 has a selective reflector 60 and a reflecting means 80.

Of these, the selective reflector 60 is configured to selectively reflect the image light Li to adjust the optical path of the image light Li, while transmitting most of the unnecessary external light Lx incident on the display device 10. Has been done. That is, the selective reflector 60 is a member expected to have a function of separating the optical path of the image light Li and the optical path of unnecessary external light Lx. By providing the selective reflector 60, it is possible to effectively prevent the external light Lx from advancing to the image forming apparatus 30. On the other hand, the reflecting means 80 is not provided with a function of separating the image light Li and the external light Lx. The reflecting means 80 may be configured as, for example, a reflecting mirror. In particular, in the illustrated example, the reflecting means 80 is configured as a concave mirror 81. By using the concave mirror 81, it is possible to magnify and project the image formed by the image forming apparatus 30. However, the guiding means 55 is not limited to the illustrated example, and may include, for example, an optical element such as a prism in place of the reflecting means 80 or in addition to the reflecting means 80.

Hereinafter, the selective reflector 60 of the guiding means 55 will be described in more detail. As shown in FIG. 2, the selective reflection plate 60 has a base material 61 and a polarizing selective reflection layer 70 laminated on the base material 61. The polarization selective reflection layer 70 has a property of selectively reflecting the image light Li to change the optical path of the image light. That is, the polarization selective reflection layer 70 distinguishes the image light Li from some other light and reflects the image light with a higher reflectance than any other light. In the illustrated example, the polarization selective reflection layer 70 reflects the image light Li with a reflectance higher than that of the external light Lx. Further, the polarization selective reflection layer 70 has a property of selectively transmitting external light Lx. That is, the polarization selective reflection layer 70 distinguishes the external light Lx from some other light, and transmits the external light Lx with a higher transmittance than any other light. In the illustrated example, the polarization selective reflection layer 70 transmits the external light Lx with a higher transmittance than the image light Li.

As a specific configuration, the polarization selective reflection layer 70 includes a plurality of cholesteric liquid crystal structure layers having a cholesteric liquid crystal structure. The cholesteric liquid crystal structure layer is composed of a liquid crystal composition exhibiting cholesteric regularity, and the director of the liquid crystal molecules is continuously rotated in the thickness direction of the layer as the physical molecular arrangement of the liquid crystal molecules in the cholesteric liquid crystal structure. It has a spiral structure. The cholesteric liquid crystal structure has a polarization separation characteristic that separates a unidirectional circularly polarized light component and a circularly polarized light component in the opposite direction based on the physical molecular arrangement of such liquid crystal molecules. .. That is, in the cholesteric liquid crystal structure, the unpolarized light incident along the spiral axis is separated into two polarized light (right circularly polarized light and left circularly polarized light), one of which is transmitted and the other is reflected. .. This phenomenon is known as circular dichroism, and when the spiral winding direction in the spiral structure of the liquid crystal molecule is appropriately selected, the circularly polarized light component having the same optical rotation direction as the spiral winding direction is selectively reflected.

The maximum optical rotation light scattering in this case occurs at _{the wavelength λ 0 of the following equation (1).}
λ ₀ = nav ・ p… (1)
Here, p is the spiral pitch length (length per pitch of the molecular spiral of the liquid crystal molecule) in the spiral structure of the liquid crystal molecule, and nav is the average refractive index in the plane orthogonal to the spiral axis.

Further, the wavelength bandwidth Δλ of the reflected light at this time is expressed by the following equation (2). Here, Δn is a birefringence value.
△ λ ＝ △ n ・ p… (2)

That is, the cholesteric liquid crystal structure layer has wavelength selectivity in addition to circularly polarized light selectivity. Therefore, the light of one circular polarization component (for example, right circular polarization in the selective reflection wavelength range) belonging to the range of the wavelength band width Δλ centered on the selective reflection center wavelength λ _{0 is polarized selective reflection.} It is selectively reflected by the layer 70 (reflected at a higher transmittance than the other light), and the other light is selectively transmitted by the polarization selective reflection layer 70 (right circular polarization within the selective reflection wavelength range). It is transmitted with a higher transmittance than the light of the component).

The polarization selective reflection layer 70 reflects light in a plurality of wavelength ranges included in the visible light range (for example, a wavelength range of 380 nm to 780 nm). That is, in the examples shown in FIGS. 1 and 2, as described above, the image light Li is composed of visible light in a plurality of wavelength ranges, and the polarization selective reflection layer 70 corresponds to the light in the plurality of wavelength ranges. It contains at least two or more cholesteric liquid crystal structural layers having different spiral pitch lengths discontinuously. For example, the image forming apparatus 30 generally realizes color display by light in a wavelength range of red (R), green (G), and blue (B), which are the three primary colors of light. Therefore, for example, light existing in the range of the selective reflection center wavelengths of 430 to 460 nm, 540 to 570 nm, and 580 to 620 nm is selectively selected based on the case where the light is vertically incident on the polarized light selective reflection layer 70. The spiral pitch length of the cholesteric liquid crystal structure is determined for the plurality of cholesteric liquid crystal structure layers included in the polarization selective reflection layer 70 so as to reflect light.

The cholesteric liquid crystal structure of the cholesteric liquid crystal structure layer has an optical characteristic that the selective reflection wavelength range shifts to the short wavelength side (so-called "blue shift") when light is obliquely incident. Therefore, it is preferable to appropriately adjust the spiral pitch length of the cholesteric liquid crystal structure according to the incident angle of the image light Li incident on the selective reflector 60 from the image forming apparatus 30.

In the example shown in FIG. 2, the polarization selective reflection layer 70 includes the first cholesteric liquid crystal structure layer 71 that selectively reflects the light of the right circularly polarized light component in the red (R) wavelength region, and the green (G). A second cholesteric liquid crystal structure layer 72 that selectively reflects the light of the right circularly polarized light component in the wavelength range, and a third cholesteric liquid crystal structure layer that selectively reflects the light of the right circularly polarized light component in the blue (B) wavelength range. 73 and. The first cholesteric liquid crystal structure layer 71, the second cholesteric liquid crystal structure layer 72, and the third cholesteric liquid crystal structure layer 73 are arranged in this order from the light input side of the polarization selective reflection layer 70.

The thickness of the cholesteric liquid crystal structure layers 71, 72, 73 shall be such that the light of the specific circularly polarized light component that is selectively reflected is reflected approximately 100% (the size is such that the reflectance is saturated). Is preferable. The reflectance of the cholesteric liquid crystal structure layer directly depends on the number of spiral pitches, but if the spiral pitch length is fixed, it indirectly depends on the thickness of the cholesteric liquid crystal structure layer. Specifically, since it is said that about 4 to 10 pitches are required to obtain 100% reflectance, a material for forming a cholesteric liquid crystal structure layer (for example, a liquid crystal composition exhibiting cholesteric regularity). Although it depends on the type of material and the selective reflection wavelength range, for example, if it is a layer of cholesteric liquid crystal structure layer that reflects light in any of the wavelength ranges of red (R), green (G) and blue (B). It preferably has a thickness of about 1 to 10 μm. On the other hand, the thicker the cholesteric liquid crystal structure layer, the better, and if it is too thick, it becomes difficult to control the orientation, unevenness occurs, and the degree of light absorption by the material itself is high. The above range is appropriate as it will be large.

As a specific example, the first cholesteric liquid crystal structure layer 71 reflects unpolarized light in the wavelength range of 600 nm or more and 700 nm or less with a reflectance of 30% or more, and the second cholesteric liquid crystal structure layer 72 reflects 450 nm or more and 550 nm or less. The unpolarized light in the wavelength range of 30% or more is reflected, and the third cholesteric liquid crystal structure layer 73 reflects the unpolarized light in the wavelength range of 300 nm or more and 400 nm or less with a reflectance of 30% or more. You may do so.

The image forming apparatus 30 may realize color display by light in a wavelength range of four or more colors. For example, the image forming apparatus 30 may realize color display by light in a wavelength range of deep red (DR), red (R), green (G), light blue (LB), and blue (B). In this case, for example, the selective reflection center wavelengths are 430 to 460 nm, 490 nm to 520 nm, 540 to 570 nm, 580 to 620 nm, and 640 to 680 nm, based on the case where light is incident perpendicular to the polarized light selective reflection layer 70. The spiral pitch length of the cholesteric liquid crystal structure may be determined for the plurality of cholesteric liquid crystal structure layers included in the polarization selective reflection layer 70 so as to selectively reflect the light existing in the range.

In the display device 10 described above, the polarizing selective reflection layer 70 selectively reflects the image light Li and transmits light in a wavelength range different from the image light Li and light having a circularly polarized light component different from the image light Li. As a result, the external light Lx, particularly sunlight, incident on the inside of the moving body main body 2 via the front glass 30 travels in the opposite direction in the optical path of the image light Li, and an optical film having low heat resistance (for example, upper polarizing) is used. It is possible to reduce the possibility of incident light on the image forming apparatus 30 including the plate 32c). Specifically, most of the external light Lx traveling in the opposite direction in the optical path of the image light Li passes through the polarization selective reflection layer 70. Therefore, the external light Lx reflected by the polarization selective reflection layer 70 and incident on the image forming apparatus 30 is only a small amount. That is, according to the present embodiment, it is possible to effectively deal with a problem that the image forming apparatus 30 is damaged by heating due to external light irradiation.

Further, in Patent Document 1, the external light Lx is prevented from being incident on the image forming apparatus 30 by diffusing the external light Lx. However, when the external light Lx is diffused in the housing 20 of the display device 10, the contrast of the image is lowered. On the other hand, in the above-mentioned display device 10, the image forming apparatus 30 reduces the possibility that the external light Lx is incident on the image forming apparatus 30 without using the means for diffusing the external light Lx. Therefore, the problem of contrast reduction due to the diffusion of external light is avoided.

Further, as shown in the example shown in FIG. 2, the selective reflector 60 includes a base material 61, three cholesteric liquid crystal structure layers 71, 72, 73 laminated on the base material 61, and a base material. It may have an absorption layer 62 laminated on the side opposite to the cholesteric liquid crystal structure layers 71, 72, 73 of 61. The absorption layer 62 functions as a beam stopper, and the external light Lx can be recovered without being diffused in the housing 20. As a result, it is possible to extremely effectively prevent the contrast decrease due to the diffusion of external light. The absorption layer 62 is not particularly limited, and a member capable of absorbing visible light and infrared rays (a concept including near infrared rays) can be used. Specifically, a black light-absorbing rubber material, an inorganic oxide (for example, black alumite-treated aluminum) or the like can be used. Further, in order to prevent the absorption layer from being heated, it is also effective to install the heat radiation fins in the absorption layer 62 or to provide a cooling means such as a blower fan.

By the way, in the display device 10, as described above, the image light Li from the image forming apparatus 30 is incident on the polarization selective reflection layer 70 diagonally, that is, at an incident angle larger than 0 °. Here, the incident angle is an angle formed by the incident direction of the image light Li and the normal direction of the light incoming surface 70a of the polarization selective reflection layer 70. Here, according to the findings obtained by the present inventors, when the image light is obliquely incident on the laminated body formed by laminating a plurality of cholesteric liquid crystal structural layers, the image light is not reflected as desired. There is. That is, in some of the cholesteric liquid crystal structure layers contained in the laminated body, the light in the wavelength range to be reflected by the layer may not be reflected as desired. In particular, it has been found that in the cholesteric liquid layer structure layer arranged at a place away from the incoming surface of the laminated body, the reflectance of light in the wavelength range to be reflected by the layer tends to decrease. It was also found that such a phenomenon becomes more remarkable as the incident angle of the image light is larger.

However, as a result of diligent research by the inventors of the present invention, by arranging a compensating layer having in-plane birefringence between a plurality of cholesteric liquid crystal structure layers contained in the laminated body, the light entering surface of the laminated body is arranged. It has been found that in the cholesteric liquid crystal structure layer arranged at a position away from the above, it is suppressed that the light in the wavelength range to be reflected by the layer is not reflected as desired. This is considered to be due to the following reasons.

That is, the light obliquely incident on the cholesteric liquid crystal structure layer undergoes phase modulation when it passes through the layer, and its polarization state changes. Then, when light is obliquely incident on the laminated body in which a plurality of cholesteric liquid crystal structure layers are laminated, phase modulation is brought to the light each time it passes through the cholesteric liquid crystal structure layer, and the polarization state is also applied to the light. It changes by the amount of phase modulation that has been applied. As a result, for example, the light incident on the laminated body as the light of the right circularly polarized light component is the light of the right elliptically polarized light component or when it is incident on the cholesteric liquid crystal structure layer arranged at a position away from the incoming surface of the laminated body. It is converted to light of a linearly polarized light component, and in some cases, light of a left circularly polarized light component. Here, the cholesteric liquid crystal structure layer contained in the laminated body is usually designed to reflect the light of a specific circularly polarized light component contained in the light incident on the laminated body. Therefore, if the polarization state of the light incident on the laminate changes, the cholesteric liquid crystal structure layer contained in the laminate cannot reflect the light incident on the layer as desired. As described above, in the cholesteric liquid crystal structure layer arranged at a position away from the light entering surface of the laminate, light having a different polarization state from the light incident on the laminate is incident, so that the light incident on the layer is incident. Cannot be reflected as desired. However, a compensating layer having in-plane birefringence is arranged between a plurality of cholesteric liquid crystal structural layers contained in the laminated body, and the compensating layer is applied to light transmitted through the cholesteric liquid crystal structural layer and undergoing phase modulation. Can bring about phase modulation to correct the phase difference of the light. For example, the light incident as the light of the right circularly polarized light component, transmitted through the cholesteric liquid crystal structure layer, and converted into the light of the right elliptically polarized light component, is transmitted through the compensation layer, so that the light is transmitted to the light of the right circularly polarized light component. Can be approached to. As a result, even in the cholesteric liquid crystal structure layer arranged at a position away from the light entering surface of the laminated body, it is possible to inject light in a polarized state close to the polarized state when it is incident on the laminated body. As a result, the reflectance of light in the layer can be improved.

Therefore, the polarization selective reflection layer 70 shown in FIG. 2 includes a compensation layer 90 having in-plane birefringence arranged between a plurality of cholesteric liquid crystal structure layers 71, 72, 73. The compensating layer 90 may be arranged between any two adjacent cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers 71, 72, 73. In the example shown in FIG. 2, the compensation layer 90 is arranged between the second cholesteric liquid crystal structure layer 72 and the third cholesteric liquid crystal structure layer 73, but is not limited thereto. The compensation layer 90 may be arranged between the first cholesteric liquid crystal structure layer 71 and the second cholesteric liquid crystal structure layer 72. The amount of phase modulation (amount of retardation) by the compensation layer 90 depends on the amount of phase modulation modulated by the cholesteric liquid crystal structure layers 71 and 72 located on the light receiving side of the compensation layer 90 in the polarization selective reflection layer 70. It is determined. Further, the polarization selective reflection layer 70 may have a plurality of compensation layers 90. In this case, as shown in FIG. 3, the compensation layer 90 may be arranged between the cholesteric liquid crystal structure layers 71, 72, 73.

The compensation layer 90 is, for example, a retardation film having positive A plate characteristics or negative A plate characteristics. A retardation film having positive A plate characteristics has an in-plane main refractive index nx (slow phase axis direction) and ny (phase advance axis direction), and the refractive index distribution is nz when the refractive index in the thickness direction is nz. A retardation film that satisfies nx> ny = nz. Further, the retardation film having a negative A plate characteristic means a retardation film having a refractive index distribution satisfying nx = nz> ny. In addition, ny = nz includes not only the case where ny and nz are completely the same, but also the case where ny and nz are substantially the same. Further, nx = nz includes not only the case where nx and nz are completely the same, but also the case where nx and nz are substantially the same. A retardation film having positive A plate characteristics and negative A plate characteristics can be produced by a known method.

The cholesteric liquid crystal structure layers 71, 72, 73 and the compensation layer 90 can be distinguished from each other by using a scanning electron microscope or a transmission electron microscope. Specifically, in the case of the cholesteric liquid crystal structural layers 71, 72, 73, it is possible to observe the structure formed by the liquid crystal molecules by using a scanning electron microscope or a transmission electron microscope. For example, when the cross section of the cholesteric liquid crystal structure layer is observed through a scanning electron microscope, a change in shading along the spiral axis of the liquid crystal molecules forming the spiral structure is observed. On the other hand, in the case of the compensation layer 90, such a structure (for example, a change in shading along the spiral axis) is not confirmed.

Next, with reference to FIGS. 4 to 6, the reflection characteristics of the laminate in which the compensation layer is arranged between the cholesteric liquid crystal structure layers and the laminate in which the compensation layer is not arranged between the cholesteric liquid crystal structure layers. An example of the difference between the reflection characteristics and the reflection characteristics will be described.

FIG. 4 is a vertical sectional view of a laminated body in which a compensation layer is arranged between the cholesteric liquid crystal structure layers. The laminate 170 shown in FIG. 4 has a 1/4 wavelength retardation layer 150, a cholesteric liquid crystal structure layer 171 having a selective reflection center wavelength at 550 nm, and a cholesteric liquid crystal having a selective reflection center wavelength at 650 nm, in this order from the incoming light side. The structure layer 172, the compensation layer 190, the cholesteric liquid crystal structure layer 173 having a selective reflection center wavelength at 600 nm, the cholesteric liquid crystal structure layer 174 having a selective reflection center wavelength at 450 nm, and the cholesteric liquid crystal having a selective reflection center wavelength at 500 nm. It has a structural layer 175 and a glass base material 161. The compensation layer 190 is a retardation film having positive A plate characteristics, and the amount of retardation thereof is 80 nm. FIG. 5 is a vertical sectional view of a laminated body in which a compensation layer is not arranged between the cholesteric liquid crystal structure layers. The laminated body 1170 shown in FIG. 5 is different from the laminated body 170 shown in FIG. 4 only in that it does not have the compensation layer 190.

FIG. 6 shows the reflection characteristics of the laminated bodies 170 and 1170 shown in FIGS. 4 and 5. The reflection characteristic shown in FIG. 6 is a measured value when the light of one of the linearly polarized light components is incident on the 1/4 wavelength retardation layer 150 at an incident angle of 30 degrees. Here, the incident direction of the incident light was as follows. That is, the incident direction in which the incoming light incident surface 170a of the laminated body 170 and the surface along both the traveling direction of the incident light and the traveling direction of the reflected light intersect is along the slow axis direction of the compensation layer 190. It was a direction. The reflection characteristics were measured using V-670 manufactured by JASCO Corporation. In FIG. 6, the reflection characteristic of the laminate 170 having the compensation layer 190 is shown by a solid line, and the reflection characteristic of the laminate 1170 without the compensation layer 190 is shown by a broken line.

As can be seen from the broken line in FIG. 6, the reflectance of the laminated body 1170 without the compensation layer 190 is different for each wavelength range. Specifically, the reflectance of the laminated body 1170 is approximately 93% in the wavelength range of 510 to 560 nm, approximately 87% in the wavelength range of 610 to 650 nm, and approximately 82% in the wavelength range of 570 to 610 nm. It is about 76% in the wavelength range of 430 to 460 nm and about 65% in the wavelength range of 470 to 500 nm. This is because the cholesteric liquid crystal structure layers 171 and 172 arranged at positions close to the light entry surface 1170a of the laminated body 1170 can reflect the light of the selective reflection center wavelength with high reflectance, but the light entry surface. The cholesteric liquid crystal structural layer 173, 174, 175 arranged at a position away from 1170a shows that the reflectance of light having the selective reflection center wavelength is low.

On the other hand, as can be seen from the solid line in FIG. 6, the reflectance of the laminated body 170 having the compensating layer 190 is generally higher than the reflectance of the laminated body 1170 having no compensating layer 190. In particular, the reflectance is greatly improved in the wavelength range of 570 to 610 nm, the wavelength range of 430 to 460 nm, and the wavelength range of 470 to 500 nm. This indicates that in the cholesteric liquid crystal structure layers 173, 174, 175 in which the light transmitted through the compensation layer 190 is incident, the reflectance of the light having the selective reflection center wavelength is improved. Therefore, by arranging the compensation layer 190 between the cholesteric liquid crystal structure layers 171, 172, 173, 174, and 175, in the cholesteric liquid crystal structure layer 173, 174, 175 arranged at a position away from the light entering surface 170a, It is understood that the reflectance of light in the selected wavelength range can be improved.

Further, referring to FIGS. 7 to 9, the reflection characteristics of the laminate in which the compensation layer is arranged between the cholesteric liquid crystal structure layers and the reflection of the laminate in which the compensation layer is not arranged between the cholesteric liquid crystal structure layers. Other examples of characteristics and differences will be described.

FIG. 7 is a vertical sectional view of a laminated body in which a compensation layer is arranged between the cholesteric liquid crystal structure layers. The laminate 270 shown in FIG. 7 has a 1/4 wavelength retardation layer 250, a cholesteric liquid crystal structure layer 271 having a selective reflection center wavelength at 600 nm, and a cholesteric liquid crystal having a selective reflection center wavelength at 500 nm, in this order from the incoming light side. Structural layer 272, compensation layer 290, cholesteric liquid crystal structural layer 273 having a selective reflection center wavelength at 550 nm, cholesteric liquid crystal structural layer 274 having a selective reflection center wavelength at 650 nm, and cholesteric liquid crystal having a selective reflection center wavelength at 450 nm. It has a structural layer 275 and a glass base material 261. The compensation layer 290 is a retardation film having positive A plate characteristics, and the amount of retardation thereof is 60 nm. FIG. 8 is a vertical sectional view of a laminated body in which a compensation layer is not arranged between the cholesteric liquid crystal structure layers. The laminated body 1270 shown in FIG. 8 is different from the laminated body 270 shown in FIG. 7 only in that it does not have the compensation layer 290.

FIG. 9 shows the reflection characteristics of the laminated bodies 270 and 1270 shown in FIGS. 7 and 8. The reflection characteristic shown in FIG. 9 is a measured value when the light of one linearly polarized light component is incident on the 1/4 wavelength retardation layer 250 at an incident angle of 30 degrees. Here, the incident direction of the incident light was as follows. That is, the incident direction in which the incoming light 270a of the laminated body 270 and the surface along both the traveling direction of the incident light and the traveling direction of the reflected light intersect is along the slow axis direction of the compensation layer 290. It was a direction. The reflection characteristics were measured using V-670 manufactured by JASCO Corporation. In FIG. 9, the reflection characteristic of the laminated body 270 having the compensation layer 290 is shown by a solid line, and the reflection characteristic of the laminated body 1270 without the compensation layer 290 is shown by a broken line.

As can be seen from the broken line in FIG. 9, the reflectance of the laminated body 1270 without the compensation layer 290 is significantly different for each wavelength range. Specifically, the reflectance of the laminated body 1270 is approximately 92% in the wavelength range of 570 to 610 nm, approximately 90% in the wavelength range of 480 to 510 nm, and approximately 76% in the wavelength range of 530 to 560 nm. In the wavelength range of 640 to 660 nm, it is about 66%, and in the wavelength range of 430 to 460 nm, it is about 78%. This is because the cholesteric liquid crystal structure layer 271,272 arranged at a position close to the light entry surface 1270a of the laminated body 1270 can reflect the light of the selective reflection center wavelength with a high reflectance, but the light entry surface. In the cholesteric liquid crystal structure layer 273, 274, 275 arranged at a position away from 1270a, it is shown that the reflectance of light having the selective reflection center wavelength is low.

On the other hand, as can be seen from the solid line in FIG. 9, the reflectance of the laminated body 270 having the compensating layer 290 is generally improved as compared with the reflectance of the laminated body 1270 having no compensating layer 290. There is. In particular, the reflectance is greatly improved in the wavelength range of 570 to 610 nm, the wavelength range of 530 to 560 nm, the wavelength range of 640 to 660 nm, and the wavelength range of 430 to 460 nm. This indicates that in the cholesteric liquid crystal structure layer 273, 274, 275 in which the light transmitted through the compensation layer 290 is incident, the reflectance of the light having the selective reflection center wavelength is improved. Therefore, by arranging the compensation layer 290 between the cholesteric liquid crystal structure layers 271,272,273,274,275, in the cholesteric liquid crystal structure layer 273,274,275 arranged at a position away from the light entering surface 270a. It is understood that the reflectance of light in the selected wavelength range can be improved.

Next, the operation of the display device 10 having the above configuration will be described.

First, the image light Li is emitted from the image forming apparatus 30. The image forming device 30 is a liquid crystal display device 31. Therefore, the image light Li is composed of light having a linearly polarized light component corresponding to the direction of the transmission axis of the upper polarizing plate 32c of the liquid crystal display device 31. As shown in FIGS. 1 and 2, the image light Li emitted from the image forming apparatus 30 then passes through the 1/4 wavelength retardation layer 50. The 1/4 wavelength phase difference layer 50 brings about 1/4 wavelength phase modulation for the image light Li. As a result, the polarized state of the image light Li is converted from one linearly polarized light to one circularly polarized light, for example, right-handed circularly polarized light.

The image light Li transmitted through the 1/4 wavelength retardation layer 50 is directed to the selective reflector 60. As shown in FIG. 2, the selective reflector 60 has a first cholesteric liquid crystal structure layer 71, a second cholesteric liquid crystal structure layer 72, a compensation layer 90, and a third cholesteric liquid crystal structure layer 73 in this order from the incoming light side. There are. The cholesteric liquid crystal structure layer is a layer having a cholesteric liquid crystal structure, has wavelength selectivity and circularly polarized light selectivity, and can selectively reflect image light Li. The compensating layer 90 has in-plane birefringence and has different refractive indexes in two non-parallel directions along the plane direction of the compensating layer 90. Therefore, the compensation layer 90 is phase-modulated so as to correct the phase difference with respect to the image light Li that has undergone phase modulation through the first cholesteric liquid crystal structure layer 71 and the second cholesteric liquid crystal structure layer 72. Can bring. Therefore, the image light Li whose phase difference is corrected by the compensation layer 90 is incident on the third cholesteric liquid crystal structure layer 73. The image light Li reflected by the selective reflector 60 is then magnified and reflected by the reflecting means 80. The image light Li magnified and reflected by the reflecting means 80 passes through the transparent cover 25 and is emitted from the display device 10. The image light Li is then reflected by the windshield 3 and is observed by the driver or the operator who is the observer.

Further, in the illustrated example, the image light finally observed is composed of one of the circularly polarized light components. Therefore, the image can also be observed by an observer wearing polarized sunglasses.

In the above-described embodiment described above, the display device 10 includes an image forming device 30 that emits image light Li and a polarizing selective reflection layer 70 that reflects image light Li to change the optical path of image light Li. And have. The polarization selective reflection layer 70 is a surface arranged between a plurality of cholesteric liquid crystal structure layers 71, 72, 73 and two cholesteric liquid crystal structure layers 72, 73 included in the plurality of cholesteric liquid crystal structure layers 71, 72, 73. It includes a compensating layer 90 having internal birefringence. The compensation layer 90 has, for example, a positive A plate characteristic or a negative A plate characteristic.

In such a display device 10, even if the image light Li is obliquely incident on the polarization selective reflection layer 70, the image light can be reflected as desired. That is, in a reflective layer in which a plurality of cholesteric liquid crystal structure layers are usually laminated, when light is obliquely incident, the cholesteric liquid crystal structure layer arranged at a position away from the light entry surface of the reflective layer is usually There is a possibility that the reflectance of light in a desired wavelength range is lowered, and the light cannot be reflected as desired by the entire reflective layer. On the other hand, in the above-described embodiment, the polarization selective reflection layer 70 is an in-plane birefringence arranged between two cholesteric liquid crystal structure layers 72, 73 included in the plurality of cholesteric liquid crystal structure layers 71, 72, 73. It includes a compensating layer 90 having sex. As a result, it is possible to prevent the desired light from being reflected as desired in the cholesteric liquid crystal structure layer 73 arranged at a position away from the light entry surface 70a of the polarization selective reflection layer 70. Therefore, even if the image light Li is obliquely incident on the polarization selective reflection layer 70, the image light can be reflected as desired. As a result, the display device 10 can obtain a display of a desired color. The compensation layer 90 may be arranged between two adjacent cholesteric liquid crystal structure layers 72, 73 included in the plurality of cholesteric liquid crystal structure layers 71, 72, 73.

In addition, in the display device 10, the polarization selective reflection layer 70 reflects the image light Li, while transmitting light having a circularly polarized light component different from the image light Li and light in a wavelength range different from the image light Li. be able to. Since the cholesteric liquid crystal structure layer forming the polarization selective reflection layer 70 has wavelength selectivity, the optical path of the image light Li such as infrared rays (concept including near infrared rays) and visible light in a wavelength range different from that of the image light Li is reversed. Most of the external light Lx incident on the display device 10 is transmitted through the polarization selective reflection layer 70. As a result, it is possible to effectively prevent a large amount of external light Lx from being incident on the image forming apparatus 30. Then, the image forming apparatus 30 can be effectively prevented from being heated by external light and causing damage.

Further, in the display device 10, unnecessary light incident on the display device 10 is deflected from the image forming device 30 by transmitting the polarization selective reflection layer 70 instead of the reflection. Therefore, it is possible to effectively prevent unnecessary light from being emitted from the display device 10 along an optical path similar to that of the image light Li. Then, it is possible to effectively avoid image deterioration due to a decrease in contrast caused by this unnecessary light. Further, most of the unnecessary light deflected from the image forming apparatus 30 can be recovered after passing through the polarization selective reflection layer 70. Thereby, deterioration of the image caused by the external light Lx incident on the display device 10 can be more effectively prevented.

Further, when the polarized light selective reflection layer 70 is manufactured, a cholesteric liquid crystal structure layer having a selective reflection wavelength region in the wavelength region of the image light Li in the visible light wavelength region may be prepared. Even in the full-color display device 10, the wavelength range of the image light Li is limited. Therefore, the polarization selective reflection layer 70 does not need to include a large number of cholesteric liquid crystal structure layers, and typically, it is sufficient for the color display display device 10 to include three cholesteric liquid crystal structure layers having different selective reflection wavelength ranges. be. Therefore, it is possible to effectively prevent the polarization selective reflection layer from being multi-layered, complicated, and expensive.

Further, the image formed by the light of the circularly polarized component can be visually recognized even through polarized sunglasses. From the above, the display device 10 according to the present embodiment is suitable for the moving body 1 in which an environment in which external light is easily incident is provided.

Further, in the above-described embodiment, the display device 10 has a 1/4 wavelength retardation layer 50 arranged at a position on the optical path of the image light Li from the layer forming device 30 to the polarization selective reflection layer 70. I have more. When the image light Li emitted by the image forming apparatus 30 is light of one linearly polarized light component, typically, when the image forming apparatus 30 is a liquid crystal display device 31, a laser projector, or the like, up to the polarization selective reflection layer 70. The image light Li can be converted into light having a circularly polarized light component that is selectively reflected by the polarization selective reflection layer 70 by the 1/4 wavelength retardation layer 50 arranged on the optical path of the above. Therefore, it is possible to enjoy the above-mentioned excellent effects while appropriately selecting the image forming apparatus 30.

Further, in the above-described embodiment, the image forming apparatus 30 emits the image light Li composed of the light of one of the linearly polarized light components. The image light Li composed of the light of one linearly polarized light component can be converted into a circularly polarized light component by using the 1/4 wavelength retardation layer 50. Therefore, the image light Li emitted from the image forming apparatus 30 can be used with high utilization efficiency.

It is possible to make various changes to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding portions in the above-described embodiment are used for the portions that can be configured in the same manner as in the above-described embodiment, and duplicates thereof are used. The explanation to be done is omitted.

For example, in the example shown in FIG. 2, the absorption layer 62 may be laminated on the side opposite to the cholesteric liquid crystal structure layers 71, 72, 73 of the base material 61, and the external light Lx is housed 20 by the absorption layer 62. It has been stated that it can be recovered without spreading within, but it is not limited to this. As another example of the method for processing the external light Lx, in the example shown in FIG. 10, the external light Lx transmitted through the selective reflector 60 is induced separately from the guiding means 55 for inducing the image light Li. External light guiding means 63 for this purpose is provided. The external light guiding means 63 may have various elements for guiding light, such as a lens, a prism, a reflecting mirror, and the like. In the example shown in FIG. 10, the external light guiding means 63 is composed of a reflecting mirror that bends the optical path of the external light Lx. The external light guiding means 63 guides the external light Lx to the outside of the housing 20 through the discharge opening 22 provided in the housing 20. However, the present invention is not limited to this example, and the external light Lx may be guided to the heat radiation fins provided for cooling the image forming apparatus 30 or the cooling system installed in the moving body main body 2. In the example shown in FIG. 10, the discharge opening 22 is covered with a lid material 22a that transmits visible light. The lid material 22a is capable of transmitting external light Lx and prevents dust and the like from entering the housing 20.

Further, as shown in FIG. 11, the display device 10 further includes a 1/4 wavelength retardation layer 51 arranged at a position on the optical path of the image light reflected by the polarization selective reflection layer 70. May be good. According to the 1/4 wavelength retardation layer 51, the image light Li reflected by the polarization selective reflection layer 70 can be converted from the circularly polarized light component to the light of the linearly polarized light component. Various optical applications can be easily applied to the image light Li having a linearly polarized light component.

Further, as shown in FIG. 11, the polarizing element 27 arranged on the optical path of the image light Li after the display device 10 is reflected by the polarization selective reflection layer 70 and transmitted through the 1/4 wavelength retardation layer 51 is further added. You may have it. The polarizing element 27 may be either an absorbing type polarizing element 27a or a reflective type polarizing element 27b. In the example shown in FIG. 11, instead of the transparent cover 25 in the above-described embodiment, the absorption type polarizing element 27a or the reflection type polarizing element 27b is installed in the opening 21 of the housing 20. The absorption type polarizing element 27a decomposes the incident light into two orthogonal polarizing components (P wave and S wave) and vibrates in one direction (direction parallel to the transmission axis) (for example, P wave). ), And has a function of absorbing a linearly polarized light component (for example, an S wave) that vibrates in the other direction (direction parallel to the absorption axis) orthogonal to the one direction. Further, the reflective polarizing element 27b decomposes the incident light into two orthogonal polarizing components (P wave and S wave) and vibrates in one direction (direction parallel to the transmission axis) (for example, a linear polarizing component (for example). It has a function of transmitting a P wave) and reflecting a linearly polarized light component (for example, an S wave) that vibrates in the other direction (direction parallel to the absorption axis) orthogonal to the one direction.

In the example shown in FIG. 11, the image light Li is converted from a circularly polarized light component to a linearly polarized light component by passing through the 1/4 wavelength retardation layer 51. If the absorption type polarizing element 27a or the reflection type polarizing element 27b is arranged so that the light of the linearly polarized light component forming the image light Li can be transmitted, the utilization efficiency of the image light Li does not decrease. Further, it was confirmed that the reflectance of the windshield 3 is higher when the image light Li is linearly polarized light (for example, S wave) than when it is circularly polarized light, and the image light Li can be effectively used. .. In this respect as well, it is effective to provide a 1/4 wavelength retardation layer on the optical path of the image light Li reflected by the polarization selective reflection layer 70.

On the other hand, in the example shown in FIG. 11, only half of the external light Lx can pass through the absorption type polarizing element 27a or the reflection type polarizing element 27b. Therefore, the amount of external light Lx incident on the housing 20 of the display device 10 can be significantly reduced while maintaining the utilization efficiency of the image light Li. This makes it possible to more effectively prevent the temperature rise of the image forming apparatus 30 and the contrast decrease of the image without affecting the brightness of the image.

As with the transparent cover 25 described above, an infrared reflective film may be laminated on the polarizing element 27.

Further, as shown in FIG. 12, the display device 10 is on the optical path of the image light Li from the layer forming device 30 to the polarization selective reflection layer 70 and is polarized instead of the above-mentioned 1/4 wavelength retardation layer 50. A 1/4 wavelength retardation layer 52 arranged at a position on the optical path of the image light Li reflected by the selective reflection layer 70 may be further provided. According to this example, when the image light Li emitted by the image forming apparatus 30 is light of one linearly polarized light component, typically, when the image forming apparatus 30 is a liquid crystal display device 31, a laser projector, or the like. The image light Li is converted into light having a circularly polarized light component that is selectively reflected by the polarization selective reflection layer 70 by the 1/4 wavelength retardation layer 52 arranged on the optical path up to the polarization selective reflection layer 70. be able to. Further, the image light Li reflected by the polarization selective reflection layer 70 can be reconverted into a linearly polarized light component by the same 1/4 wavelength retardation layer 52. As a result, the polarization state of the image light Li after the optical path is adjusted by the polarization selective reflection layer 70 can be converted into a linearly polarized light component. Various optical applications can be easily applied to the image light Li having a linearly polarized light component.

In particular, in the example shown in FIG. 12, the 1/4 wavelength retardation layer 52 is laminated on the polarization selective reflection layer 70. According to such an arrangement of the 1/4 wavelength retardation layer 52, the image light Li is 1/4 when it is incident on the polarization selective reflection layer 70 and twice after being reflected by the polarization selective reflection layer 70. The wavelength retardation layer 52 can be transmitted more reliably. Since the 1/4 wavelength retardation layer 52 can be arranged close to the polarization selective reflection layer 70, the display device 10 can be miniaturized.

Similar to the example shown in FIG. 11, in the example shown in FIG. 12, the image after the display device 10 is reflected by the polarization selective reflection layer 70 and transmitted through the 1/4 wavelength retardation layer 52. Further, a polarizing element 27 (absorbing type polarizing element 27a or reflective type polarizing element 27b) arranged on the optical path of the optical Li may be further provided. By installing the absorption type polarizing element 27a or the reflective type polarizing element 27b, as already described with reference to FIG. 11, the temperature of the image forming apparatus 30 and the temperature of the image are increased without affecting the brightness of the image. It is also possible to prevent the decrease in contrast more effectively.

Further, in the above-described embodiment, the liquid crystal display device 31 is exemplified as the image forming device 30 that emits the image light Li composed of one of the linearly polarized light components, but the present invention is not limited to this example. For example, as shown in FIG. 13, the laser projector 36 can be used as an image forming apparatus 30 that emits image light Li composed of one linearly polarized light component. The laser projector 36 shown in FIG. 13 includes a laser light source 37 that emits laser light, a scanning device 38 that changes the optical path of the laser light over time, and a screen on which laser light whose optical path is adjusted by the scanning device is incident. 39 and. The scanning device 38 adjusts the optical path of the laser beam so that the laser beam scans on the screen. An image is formed on the laser light source 37 by dividing the screen into pixel regions and controlling the emission and emission stop of the laser light from the laser light source 37 for each pixel region. By adjusting the polarization state of the laser light oscillated from the laser light source 37 to one linearly polarized light component, the laser projector 36 emits the image light Li composed of one of the linearly polarized light components from the scanning device 38. Can be done. The laser projector 36 shown in FIG. 13 is advantageous in that the utilization efficiency of the light source light is extremely high as compared with the liquid crystal display device.

Further, in the above-described embodiment, an example is shown in which the image forming apparatus 30 that emits the image light Li composed of one of the linearly polarized light components is used, but the present invention is not limited to this. It is also possible to use an image forming apparatus that emits unpolarized image light Li. When the unpolarized image light Li is incident on the polarization selective reflection layer 70, approximately half of the image light Li is reflected by the polarization selective reflection layer 70. That is, although the utilization efficiency of the image light Li is reduced, the above-mentioned effects such that the contrast reduction of the image due to the reflection of external light can be effectively prevented can be enjoyed. For example, in the laser projector 36 shown in FIG. 13, the laser light source 37 oscillates a laser beam whose polarization state is not adjusted, or the liquid crystal display device 31 shown in FIG. 2 or the laser shown in FIG. When the projector 36 includes a member having a strong diffusion function, unpolarized image light Li is emitted from the image forming apparatus 30.

Further, the image forming apparatus 41 using the digital micromirror device 44 as shown in FIG. 14 also emits unpolarized image light Li unless special means are used. The image forming apparatus 41 shown in FIG. 14 includes a light source 42 that emits unpolarized light, a prism 43, and a digital micromirror device 44. The light source 42 includes, for example, a light emitting diode, and irradiates the prism 43 with unpolarized planar light. The planar light passes through the prism 43 and is incident on the digital micromirror device 44. The digital micromirror device 44 is a MEMS element including a large number of micromirrors, and functions as a reflection type spatial light modulator. The digital micromirror device 44 forms an image by switching the reflection direction of the micromirror for each pixel. The image light Li formed by the digital micromirror device 44 is totally reflected by the prism 43 and heads toward the selective reflector 60 of the guiding means 55.

The image forming apparatus 41 shown in FIG. 14 is advantageous in that the utilization efficiency of the light source light is extremely high as compared with the liquid crystal display apparatus. Even if only about half of the image light Li can be reflected by the polarization selective reflection layer 70, the utilization efficiency of the light source light is high as a whole.

Further, in combination with the image forming apparatus 30 that emits unpolarized image light Li, it is possible to devise ways to improve the utilization efficiency of the light source light. In the example shown in FIG. 15, an image forming apparatus 30 that emits unpolarized image light Li is used, and the polarization selective reflection layer 70 has a cholesteric liquid crystal structure layer that selectively reflects light of a right circularly polarized light component and a left. It may include both a cholesteric liquid crystal structural layer that selectively reflects light of a circularly polarized light component. According to such an example, the unpolarized image light Li in the selective reflection wavelength range of the cholesteric liquid crystal structure layer can be reflected by the polarized light selective reflection layer 70 with high reflectance, and the utilization efficiency for the light source light. And the energy efficiency of the entire display device 10 can be significantly improved.

The cholesteric liquid crystal structure layer that selectively reflects the light of the right circularly polarized light component and the cholesteric liquid crystal structure layer that selectively reflects the light of the left circularly polarized light component have the winding directions of the spiral structure formed by the liquid crystal molecules opposite to each other. The cholesteric liquid crystal structure layer that selectively reflects the light of the right circularly polarized light component and the cholesteric liquid crystal structure layer that selectively reflects the light of the left circularly polarized light component have the same selective reflection center wavelength by making the pitch of the spiral structure the same. Will have. In the specific example shown in FIG. 16, the polarization selective reflection layer 70 has the first to sixth cholesteric liquid crystal structure layers 71 to 76. The first to third cholesteric liquid crystal structure layers 71, 72, 73 selectively reflect the light of the right circularly polarized light component, and the fourth to sixth cholesteric liquid crystal structure layers 74, 75, 76 are of the left circularly polarized light component. Selectively reflect light. The first cholesteric liquid crystal structure layer 71 and the fourth cholesteric liquid crystal structure layer 74 have the same selective reflection center wavelength, and selectively reflect light in the red (R) wavelength range. The second cholesteric liquid crystal structure layer 72 and the fifth cholesteric liquid crystal structure layer 75 have the same selective reflection center wavelength, and selectively reflect light in the green (G) wavelength range. The third cholesteric liquid crystal structure layer 73 and the sixth cholesteric liquid crystal structure layer 76 have the same selective reflection center wavelength, and selectively reflect light in the blue (B) wavelength range.

In this case, as shown in FIG. 16, the compensation layer 90 is located between any two adjacent cholesteric liquid crystal structural layers 75, 73 included in the plurality of cholesteric liquid crystal structural layers 71, 74, 72, 75, 73, 76. May be placed in. Further, the polarization selective reflection layer may have a plurality of compensation layers 90. In this case, for example, as shown in FIG. 17, the compensation layer 90 may be arranged between the cholesteric liquid crystal structure layers 71, 74, 72, 75, 73, 76.

Further, in the example shown in FIG. 15, the display device 10 may further have a polarizing element 27 arranged on the optical path of the image light Li after being reflected by the polarization selective reflection layer 70. The polarizing element 27 may be either an absorbing type polarizing element 27a or a reflective type polarizing element 27b. In the example shown in FIG. 18, instead of the transparent cover 25 in the display device 10 shown in FIG. 15, an absorption type polarizing element 27a or a reflection type polarizing element 27b is installed in the opening 21 of the housing 20. ..

In this example, the image light Li reduces the amount of light by about half when it passes through the polarizing element 27. However, as described above, since the energy efficiency of the image forming apparatus itself that emits the unpolarized image light Li is excellent, the energy efficiency of the display apparatus 10 as a whole is still at a high level. On the other hand, in the example shown in FIG. 18, only half of the external light Lx can pass through the polarizing element 27. Therefore, the amount of external light Lx incident on the housing 20 of the display device 10 can be significantly reduced. This makes it possible to more effectively prevent the temperature rise of the image forming apparatus 30 and the contrast decrease of the image.

Although some modifications to the above-described embodiments have been described above, it is naturally possible to apply a plurality of modifications in combination as appropriate.

Further, in the above-described embodiment and its modification, the polarizing selective reflection layer selectively reflects light in the visible light region and transmits other light (for example, infrared rays) as a so-called cold mirror for heat shielding. We have described examples used in, but are not limited to this. For example, the polarized light selective reflection layer according to the present invention may be used as a so-called hot mirror that selectively transmits light in the visible light region and reflects other light (for example, infrared rays).

Li image light Lx external light 1 moving body 2 moving body body 3 front glass 4 dashboard 4a opening 10 display device 20 housing 21 opening 22 discharge opening 25 transparent cover 30 image forming device 31 liquid crystal display device 32 liquid crystal display panel 32a lower polarizing Plate 32b Liquid crystal cell 32c Upper polarizing plate 33 Surface light source device 36 Laser projector 37 Laser light source 38 Scan device 39 Screen 41 Image forming device 42 Light source 43 Prism 44 Digital micromirror device 50 1/4 wavelength retardation layer 51 1/4 wavelength position Phase difference layer 52 1/4 wavelength retardation layer 55 Induction means 60 Selective reflector 61 Base material 62 Absorbent layer 70 Polarized selective reflective layer 71 First cholesteric liquid crystal structure layer 72 Second cholesteric liquid crystal structure layer 73 Third cholesteric liquid crystal structure layer 74 4th cholesteric liquid crystal structure layer 75 5th cholesteric liquid crystal structure layer 76 6th cholesteric liquid crystal structure layer 80 Reflective means 81 Concave mirror 90 Compensation layer

Claims (20)

An image forming device that emits image light and
A polarization selective reflection layer that reflects the image light and changes the optical path of the image light is provided.
The polarization selective reflection layer includes a plurality of cholesteric liquid crystal structure layers and a compensating layer having in-plane birefringence arranged between two cholesteric liquid crystal structure layers included in the plurality of cholesteric liquid crystal structure layers. fruit,
The amount of phase modulation by the compensating layer is determined according to the amount of phase modulation of the image light modulated by the cholesteric liquid crystal structure layer located on the incoming side of the image light in the compensating layer in the polarization selective reflection layer. ,
The compensation layer is a display device that brings the polarization state of the image light transmitted through the compensation layer closer to the polarization state of the image light when the image light is incident on the polarization selective reflection layer. The display device according to claim 1, wherein the compensation layer having in-plane birefringence is arranged between any two adjacent cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers. The display device according to claim 1 or 2, wherein the compensation layer has a positive A plate characteristic or a negative A plate characteristic. The invention according to any one of claims 1 to 3, further comprising a 1/4 wavelength retardation layer arranged at a position on the optical path of the image light from the image forming apparatus to the polarization selective reflection layer. Display device. The display device according to claim 4, further comprising a 1/4 wavelength retardation layer arranged at a position on the optical path of the image light reflected by the polarization selective reflection layer. A 1/4 wavelength retardation layer arranged at a position on the optical path of the image light from the image forming apparatus to the polarization selective reflection layer and on the optical path of the image light reflected by the polarization selective reflection layer. The display device according to any one of claims 1 to 3, further comprising. The display device according to claim 6, wherein the 1/4 wavelength retardation layer is laminated on the polarization selective reflection layer. The invention according to any one of claims 5 to 7, further comprising a polarizing element arranged on the optical path of the image light after being reflected by the polarization selective reflection layer and transmitted through the 1/4 wavelength retardation layer. Display device. The display device according to any one of claims 4 to 8, wherein the image forming apparatus emits the image light composed of light of one linearly polarized light component. The display device according to any one of claims 1 to 9, wherein the image forming device includes a liquid crystal display device. One of claims 1 to 3, wherein the polarized light selective reflection layer includes a cholesteric liquid crystal structure layer that selectively reflects light of a right circularly polarized light component and a cholesteric liquid crystal structure layer that selectively reflects light of a left circularly polarized light component. The display device according to paragraph 1. The display device according to claim 11, further comprising a polarizing element arranged on the optical path of the image light after being reflected by the polarization selective reflection layer. The image forming apparatus includes a light source, a digital micromirror device that changes the optical path of light from the light source, and a screen on which the light whose optical path is changed by the digital micromirror device is incident. The display device according to 3, 11 or 12. The image forming apparatus includes a laser light source that emits a laser beam, a scanning device that changes the optical path of the laser beam over time, and a screen to which the laser beam whose optical path is adjusted by the scanning device is incident. , The display device according to any one of claims 1 to 9. A mobile body comprising the display device according to any one of claims 1 to 14. A reflector including a plurality of cholesteric liquid crystal structural layers and a compensating layer having in-plane birefringence arranged between two cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers.
The phase modulation amount by the compensation layer is determined according to the phase modulation amount of the light modulated by the cholesteric liquid crystal structure layer located on the light input side of the compensation layer in the reflector.
The compensating layer is a reflector that brings the polarized light of the light transmitted through the compensating layer closer to the polarized state of the light when the light is incident on the reflector. 16. The reflector according to claim 16, wherein the compensating layer having in-plane birefringence is arranged between any two adjacent cholesteric liquid crystal structural layers contained in the plurality of cholesteric liquid crystal structural layers. The reflector according to claim 16 or 17, wherein the compensation layer has a positive A plate characteristic or a negative A plate characteristic. The reflector according to any one of claims 16 to 18, wherein the 1/4 wavelength retardation layer is laminated. The reflector according to any one of claims 16 to 19, comprising a cholesteric liquid crystal structure layer that selectively reflects light of a right circularly polarized light component and a cholesteric liquid crystal structure layer that selectively reflects light of a left circularly polarized light component. ..

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