JP2016122128A - Optical element and on-vehicle display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a reduction in visibility due to reflection of external light with a simple configuration without significantly impairing transmittance; and to provide an optical element that can suppress reflection of a display image without causing moire and the like and extremely narrowing a viewing angle, and an on-vehicle display device using the same.SOLUTION: There is provided a transmissive optical element 5 attached to a display device 4, the optical element including a polarizing plate 3 on a visible side, and a phase difference layer 1 and an optical activity layer 2 having optical activity between the polarizing plate 3 and the display device 4.SELECTED DRAWING: Figure 1

Description

  The present invention is mainly used in an in-vehicle display device, an optical element that suppresses a decrease in visibility due to external light reflection and prevents a night display image from being reflected on a windshield, a door glass, etc., and an in-vehicle device using the same The present invention relates to a display device.

  In-vehicle display devices are in an environment in which external light enters from the windshield, door glass, and rear glass. When external light enters the display screen, the external light incident on the screen surface is scattered and reflected (hereinafter referred to as external light). The visibility of the display image is impaired. In particular, when a design glass or touch panel is arranged on the display device surface, in addition to the reflection on the image surface, reflected light is generated on the design glass back surface, the touch panel back surface, the touch panel electrode, etc. The phenomenon of out occurs.

  As a method for suppressing such a decrease in visibility due to external light reflection, an AR (Anti Reflection Coating) antireflection layer using a multilayer deposited film is disposed on the back surface of the design glass and the back surface of the touch panel in addition to the reflection on the image surface. It is done. For example, in Patent Document 1, in a structure having a liquid crystal panel and a transparent plate facing the display surface of the liquid crystal panel, in order to eliminate a phenomenon in which external light is reflected on the transparent plate, A method of arranging an antireflection layer in which a low refractive index layer and a high refractive index layer are laminated on both surfaces and a liquid crystal display surface has been proposed. As for the antireflection layer of such an in-vehicle display device, Patent Document 2 discloses that a low refractive index material such as magnesium fluoride or silicon dioxide is used as a low refractive index layer, and titanium dioxide or zircon oxide is used as a high refractive index layer. There has been proposed a method of depositing a plurality of layers of high-refractive index materials such as nitrogen alternately by a vapor deposition method or a sputtering method with a predetermined film thickness.

  Moreover, the method of using a circularly-polarizing plate is also mentioned as a method of preventing external light reflection. In this method, a linearly polarizing plate and a quarter wavelength plate are combined vertically, and external light passes through the polarizing plate and then passes through the quarter wavelength plate to become circularly polarized light. When the light is reflected on the viewer side and passes through the quarter-wave plate, it becomes linearly polarized light having a 90-degree polarization plane rotated by being transmitted through the quarter-wave plate and is absorbed by the linearly polarizing plate to prevent reflection of external light. It is. However, in this method, when the liquid crystal display device is arranged on the front surface, the transmittance is lowered, the brightness of the image is lowered, and the visibility in a bright environment is also lowered. Furthermore, there is a problem that the hue of the image changes due to the circularly polarizing plate. For this problem, in Patent Document 3, in a touch panel attached to a liquid crystal display device, a circularly polarizing plate is disposed on the viewer side, and the circularly polarizing plate is disposed on the back side of the touch panel (between the liquid crystal display device and the touch panel). There has been proposed a method of suppressing a decrease in transmittance and a change in hue of an image by adding a quarter wavelength plate in an arrangement that cancels the phase difference of the quarter wavelength plate. In addition, a method such as installing a display device inside the bag is employed so that light does not enter the display screen.

  In addition to the problem of reduced visibility due to external light reflection, in-vehicle display devices reduce the visibility of the driver by reflecting the display image on the windshield during night driving of the vehicle. There is also a problem to make. In order to control the light from the display screen in a predetermined direction for the purpose of preventing such reflection of the display screen on the windshield, a louver-like structure manufactured by the method described in Patent Documents 4 and 5 is used. The micro louver film used has been proposed. Furthermore, in Patent Document 6, for the purpose of preventing reflection on the windshield, a retardation element made of liquid crystal or a liquid crystal polymer, and a polarizing plate on each of the retardation element and the viewing side and the non-viewing side are provided. It has been proposed to use a twisted phase difference plate in which the phase difference element is tilted.

JP 2008-256728 A JP 2000-32428 A Japanese Patent Laid-Open No. 10-186136 Japanese Patent Laid-Open No. 50-92751 JP-T-2004-514167 JP 2006-209021 A

  The low-refractive-index material and the high-refractive-index material formed by vapor deposition or sputtering as the antireflection layers described in Patent Document 1 and Patent Document 2, which have been proposed for the purpose of suppressing visibility degradation due to external light reflection When an antireflection layer composed of a multi-layered laminate is applied, it is necessary to form a multilayer deposited film on each surface of the design glass back surface and the touch panel back surface, and there is a problem that the configuration and the manufacturing process become complicated. . In the method proposed in Patent Document 3, it is necessary to dispose another quarter-wave plate in addition to the circularly polarizing plate, and this method also has problems such as a complicated configuration and manufacturing process.

  In addition, the micro louver films proposed in Patent Documents 4 and 5 which are proposed for the purpose of preventing the display screen from being reflected on the windshield are complicated and expensive in manufacturing process, and also depend on the installation angle of the louvers. However, there is a problem that moire occurs between the pixel arrangement of the display device. Furthermore, there is a problem that the viewing angle characteristic of the display screen becomes extremely narrow, and there is no effect of reducing external light reflection. The optical element by the twisted phase difference plate and the polarizing plate which is proposed in Patent Document 6 and inclined for the purpose of preventing the reflection of the same display screen on the windshield has no effect of reducing the reflection of external light.

  Other methods such as installing a display device inside the bag to prevent external light from entering the display screen or to prevent reflection on the windshield are available. There is a problem that the arrangement of the display device is limited to the inside of the bag and the design freedom around the display device is impaired.

  The present invention has been made in view of such problems. In an optical element and a vehicle-mounted display device using the optical element, an object is to suppress a reduction in visibility due to reflection of external light without greatly impairing transmittance with a simpler configuration. In addition, it is an object to provide an optical element capable of suppressing the reflection of a display image without causing moiré or the like and extremely narrowing the viewing angle, and an in-vehicle display device using the optical element.

  As a result of intensive studies to solve the above problems, the present inventor has found that the following problems can be solved by the present invention, and the present invention has been completed.

  An optical element according to the present invention is a transmissive optical element mounted on a display unit, and includes a polarizing plate on the side to be visually recognized, and a retardation layer and optical rotation between the polarizing plate and the display unit. It has the optical rotation layer which has.

  With the above-described configuration, the transmittance of the optical element according to the present invention is greatly improved by providing a retardation layer and an optical rotation layer having optical rotation between the polarizing plate and the display unit. Without impairing, it is possible to suppress a decrease in visibility due to reflection of external light, and in addition, it is possible to suppress the reflection of a display image without generating moiré or the like and extremely narrowing the viewing angle.

  Preferably, in the optical element according to the present invention, an in-plane retardation of the retardation layer is 90 nm to 185 nm with respect to light having a wavelength of 550 nm. With this configuration, a phase difference is given to the external light incident through the polarizing plate and the reflected light reflected by the external light and the display unit surface, so that at least a part of the reflected light is directed to the viewer side. Since the light is absorbed by the polarizing plate at the time of emission, it is possible to suppress external light reflection and suppress deterioration in visibility. That is, when the in-plane phase difference is less than 90 nm, the change in the polarization state of the reflected light is small, the amount of light absorbed by the polarizing plate when emitted is small, and external light reflection cannot be sufficiently suppressed. When the in-plane retardation exceeds 185 nm, the reflected light approaches the polarization state that passes through the polarizing plate, so that the amount of light absorbed by the polarizing plate is small when exiting, and external light reflection cannot be sufficiently suppressed.

  Preferably, in the optical element according to the present invention, the optical rotation angle of the optical rotatory layer is ± 20 ° to ± 80 °. With this configuration, the outgoing light from the display unit toward the viewer is efficiently converted to a polarization state that is transmitted through the polarizing plate when transmitted through the optical rotatory layer and the retardation layer, thereby suppressing a decrease in transmittance. On the other hand, since light emitted from the display unit toward the windshield can be converted into a polarization state absorbed by the polarizing plate, light directed toward the windshield can be suppressed. That is, when the absolute value of the optical rotation angle is less than 20 °, it is insufficient to efficiently convert the outgoing light from the display unit toward the viewer into a polarization state that transmits the polarizing plate, resulting in a decrease in transmittance. Furthermore, the light emitted from the display unit toward the windshield is not sufficiently converted to the polarization state absorbed by the polarizing plate, and the light directed toward the windshield cannot be suppressed. When the absolute value of the optical rotation angle exceeds 80 °, it is insufficient to efficiently convert the outgoing light from the display unit toward the viewer to a polarization state that transmits the polarizing plate, and the transmittance decreases. End up.

  Preferably, in the optical element according to the present invention, the transmission axis of the polarizing plate is set within a range of ± 15 degrees with respect to the vertical direction. With this configuration, the light emitted from the display unit and reflected on the windshield is within the range of the Brewster angle when entering the windshield, so that no reflected light can be generated, and the reflection suppression effect Can be played. Here, the vertical direction is a direction that matches the vertical direction on the screen of the display unit, and is usually a direction that also matches the vertical direction of the polarizing plate.

  Preferably, in the optical element according to the present invention, the polarizing plate, the retardation layer, and the optical rotatory layer are laminated in this order from the visually recognized side, and the transmission axis of the polarizing plate and the retardation layer The angle between the slow axis is set in a range of ± 20 degrees to ± 70 degrees. With this configuration, a phase difference can be given to external light incident through the polarizing plate, and reflection of external light can be suppressed and visibility degradation can be suppressed. That is, when the angle is less than ± 20 degrees, it is insufficient to give a phase difference to the external light, and it is not possible to suppress external light reflection and suppress deterioration of visibility. Even when the angle exceeds ± 70 degrees, it is insufficient to give a phase difference to the external light, and it is impossible to suppress the reflection of the external light and suppress the deterioration of the visibility.

  Preferably, in the optical element according to the present invention, anti-glare treatment and anti-reflection are provided on the side to be viewed, the side facing the side to be viewed, or both sides of the side to be viewed and the side facing the viewer. An antireflection layer is formed by at least one of processing and low reflection processing. With this configuration, external light reflection can be reduced.

  The vehicle-mounted display device according to the present invention is equipped with any one of the above optical elements. With this configuration, it is possible to suppress a reduction in visibility due to external light reflection without significantly impairing the transmittance with a simpler configuration, and in addition, display images can be generated without causing moiré or extremely narrowing the viewing angle. An in-vehicle display device that suppresses the reflection of the image can be used.

  The on-vehicle display device preferably includes an operation touch panel device between the display unit and the optical element. When a touch panel is arranged on the display unit, the reflected light is generated on the touch panel and thus the visibility is reduced. However, this configuration can reduce external light reflection.

  In the optical element of the present invention and the in-vehicle display device using the optical element, it is possible to suppress a decrease in visibility due to reflection of external light with a simple configuration without significantly impairing the transmittance. In addition, it is possible to suppress the reflection of the display image without generating moiré or the like or extremely narrowing the viewing angle.

It is a general | schematic disassembled perspective view which shows the optical element of one Embodiment of this invention. It is a schematic side view which shows a mode that the reflectance etc. of the optical element of the embodiment are measured with a film thickness meter. It is a schematic perspective view which shows the experiment aspect which measures the reflection prevention effect of the optical element of the embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding parts, and the description thereof is omitted as appropriate unless there is a specific change or the like.

(Basic configuration of optical element)
As shown in FIG. 1, the optical element 5 of the present embodiment includes, for example, a film-like in-plane retardation layer 1 (hereinafter also simply referred to as a retardation layer), an optical rotatory layer 2 having optical rotation, and a polarizing plate 3. And is mounted on the front surface of the in-vehicle display unit 4 arranged on the dashboard, for example. The optical element 5 and the display unit 4 constitute the display device of this embodiment. Specifically, the optical element 5 is mounted on a view area part such as a design glass of the in-vehicle display unit 4 or a touch panel TP (see, for example, an alternate long and short dash line in FIG. 1). It is desirable that it is disposed between or on the side where the view area is viewed (hereinafter also referred to as the viewer side), and is in close contact with the front or back surface of the view area without including an air layer by an adhesive or the like. Specifically, the optical element 5 includes the polarizing plate 3 on the side to be visually recognized, and includes the retardation layer 1 and the optical rotation layer 2 between the polarizing plate 3 and the display unit 4.

  The optical element 5 of the present embodiment includes an antireflection layer as necessary in addition to the polarizing plate 3, the in-plane retardation layer 1 and the optical rotation layer 2. In the configuration of the present embodiment, the incident natural light that has passed through the polarizing plate 3 attached to the viewer side of the optical element 5 becomes linearly polarized light and is transmitted through the retardation layer 1 and the optical rotation layer 2. The transmitted light has a phase difference and the plane of polarization rotates. Further, the light is reflected from the back surface of the optical element 5 and the surface of the display unit 4, and is incident again from the back surface side and passes through the retardation layer 1 and the optical rotation layer 2. The light incident on the phase difference layer 1 and the optical rotatory layer 2 again has a phase difference, and the polarization state changes as the polarization plane rotates. When the reflected light whose polarization state has changed passes through the polarizing plate 3 mounted on the viewer side of the optical element 5 again, it is absorbed and the reflection of external light can be suppressed.

(Polarizer)
In the present embodiment, the polarizing plate 3 is a plate that allows only light polarized or polarized in a specific direction to pass therethrough. FIG. 1 shows that the transmission axis n of the polarizing plate 3 is inclined by φ with respect to the vertical direction. Here, the vertical direction is a direction that matches the vertical direction on the screen of the display unit 4, and in this embodiment, the vertical direction on the surface of the polarizing plate 3 also matches the vertical direction. As such a polarizing plate 3, a monoaxially stretched polyvinyl alcohol resin film dyed with iodine or a dichroic dye is treated with boric acid, and then a protective film such as a triacetyl cellulose film is laminated on both sides or one side. Can be used.

(Retardation layer)
In the present embodiment, the retardation layer 1 is a layer that causes a retardation in transmitted light. Examples of such a retardation layer 1 include those produced by stretching a polymer material such as polycarbonate and cycloolefin polymer, those produced by aligning a liquid crystal compound on an alignment film, and JP-A-2002-202409. Or a photo-alignment material described in JP 2004-170595 A can be used. As a result of intensive studies by the present inventors, the in-plane retardation of the retardation layer 1 is preferably 90 nm to 185 nm, and more preferably 100 nm to 175 nm. Here, the value of the phase difference is a value for light having a wavelength of 550 nm. However, it is not limited to what was described here.

(Optical rotation layer)
In the present embodiment, the optical rotatory layer 2 is a layer having a property of rotating the polarization plane of linearly polarized light passing through the layer. As such an optical rotation layer 2, a substrate having an alignment film subjected to a liquid crystal alignment process such as a rubbing process or a photo-alignment process is opposed to each other, and the alignment direction of the opposed substrate is rotated by a predetermined angle. , Manufactured by a step of inducing alignment by filling a liquid crystal compound between both substrates, and applying a liquid crystal compound to a substrate on which an alignment film is formed as described in JP-A-2006-72273. Then, those manufactured by applying a magnetic field in a predetermined direction, or those manufactured by adding a chiral agent to a liquid crystal compound to form a film can be used. In addition, as a result of intensive studies by the inventors, it is preferable that the optical rotation angle of the optical rotatory layer 2 is ± 20 ° to ± 80 °. However, it is not limited to the materials or optical rotation angles described here.

(Lamination angle)
In the optical element 5 of the present embodiment, as described above, the suppression of external light reflection is performed by transmitting the polarizing plate 3 attached to the viewer side of the optical element 5 and converting the external light converted into linearly polarized light. By passing through the phase difference layer 1 and the optical rotatory layer 2, further reflecting from the back surface of the optical element 5 and the surface of the display unit 4, entering again from the back surface side, and passing through the phase difference layer 1 and the optical rotatory layer 2. This is because the phase difference is generated and the polarization plane is rotated, so that the polarization state is changed, so that the amount of emitted light is absorbed by the polarizing plate 3. From such a viewpoint, when the polarizing plate 3, the retardation layer 1, and the optical rotation layer 2 are laminated in this order from the viewer side, the transmission axis n of the polarizing plate 3 and the slow axis m of the retardation layer 1. Is preferably ± 20 degrees to ± 70 degrees (hereinafter also referred to as a bonding angle) θ. Moreover, when laminating | stacking in order of the polarizing plate 3, the optical rotatory layer 2, and the phase difference layer 1, it is preferable that the bonding angle (theta) is suitably set with the optical rotation angle of the optical rotatory layer 2, and other conditions.

(Antireflection treatment layer)
In the present embodiment, the inclined alignment film and the polarizing plate 3 are combined to suppress reflection of external light. However, the viewing side of the optical element 5 of the present embodiment or the side facing the viewing side, or the viewing side and By applying an antireflection treatment to both sides facing the viewing side, it is possible to further suppress the reflected light. Examples of the antireflection treatment layer include an antireflection (AR) treatment, a low reflection (LR) treatment, an antiglare (AG) treatment layer, and a moth-eye structure layer.

  The AR process and the LR process are formed by laminating a single layer or a plurality of films having different refractive indexes by a process of coating, drying, and curing such as vacuum deposition, sputtering, or solution coating. The light reflected on the surface with the antireflection treatment layer and the light reflected at each interface of the layers forming the antireflection layer and the interface with the material (only the interface with the base material in the case of a single layer) cancels out due to interference. On the other hand, reflection can be suppressed. In many cases, the AR processing indicates a reflectance of 1% or less, and the LR processing indicates a reflectance of about 1 to 2%.

  The AG treatment is an anti-glare treatment that forms a concavo-convex shape on the surface and diffuses reflected light, thereby blurring a reflected image by regular reflection and cutting glare. A method of coating the surface of the substrate with inorganic particles such as silica, or organic fine particles made of styrene, acrylic or a copolymer of styrene and acrylic, a transfer mold with a concavo-convex shape on the surface of the substrate, transfer by UV curing resin or heat Examples thereof include a method of forming irregularities on the surface by a saddle shape, or a method of forming irregularities by roughening the surface by a method such as sandblasting.

  The moth-eye structure is formed, for example, by forming a spindle-shaped structure on the surface with a period shorter than the wavelength. When such a structure is arranged on the surface, the light directed from the air into the base material has the same effect as the refractive index gradually changing, and there is no sharp interface where the refractive index changes. Does not occur. As such a structure, a structure formed by a nanoimprint method using a UV curable resin or a structure having a fine structure transferred by heat and pressure can be used. Moreover, it is also possible to affix the film which performed such a process separately on the surface.

[Prevention of windshield reflection]
The optical element 5 of the present embodiment is not particularly limited as long as it can display information as the combined display unit 4 in terms of suppressing external light reflection, and can provide an effect. However, regarding the windshield reflection, when the display unit on which the polarizing plate 3 is mounted on the viewer side is a liquid crystal display unit or an organic EL display unit, the light emitted from the display unit is linearly polarized. The polarization state changes between the optical rotatory layer and the retardation layer, and an effect of preventing reflection can be achieved. Depending on the axial angle of the polarizing plate 3 mounted on the viewer side, in the case of a vehicle-mounted display unit such as a center information display and arranged at the top of the dashboard, it is compared with the light emitted in the front direction. Thus, the light traveling toward the windshield, that is, the light traveling obliquely upward, is incident obliquely on the phase difference layer 1 and the optical rotation layer 2 of the optical element 5 mounted on the front surface. By transmitting 2, the polarization state changes greatly compared to light transmitted vertically. For this reason, when passing through the polarizing plate 3, the light toward the windshield is absorbed and the transmittance is lowered. From the above, according to the optical element 5 of the present embodiment, since the amount of light reaching the windshield is reduced, the effect of suppressing the reflection on the windshield is also obtained.

  Regarding the effect of preventing windshield reflection, the arrangement of the polarizing plate 3 on the viewer side of the optical element 5 affects the degree of the effect. In a general in-vehicle display unit, an angle at which reflection is reduced such that light traveling toward the windshield becomes P-polarized light with respect to the windshield and incident at a Brewster angle is further transmitted through the polarizing plate 3 in the optical element 5. It is desirable that the axis n is within a range of ± 15 ° with respect to the vertical direction, thereby reducing the amount of light reaching the windshield described above by absorbing it into the polarizing plate 3. It is possible to further suppress the reflection on the glass. When the transmission axis n of the polarizing plate 3 arranged on the viewing side of the optical element 5 is larger than ± 15 ° with respect to the vertical direction, the Brewster angle is deviated, so that reflected light is generated and reflected. The inhibitory effect may be impaired. However, it can be appropriately adjusted according to the transmission axis angle of the polarizing plate 3 mounted on the viewer side of the display unit 4, the positional relationship between the display unit 4 and the windshield, and the eye point of the viewer.

〔Example〕
The measurement results of Example 1 to Example 9 and Comparative Example 1 are summarized in Tables 1 and 2. In this example, as the polarizing plate 3, a commercially available polarizing plate in which the polarizing element is a PVA / iodine-based film and the protective film is a TAC (triacetyl cellulose) film is used. In each example, the arrangement of the polarizing plates 3, that is, the angle φ of the transmission axis n with respect to the vertical direction (the transmission axis angle φ of the polarizing plate 3) is zero degrees (φ = 0 °).

  As the retardation layer 1, a general retardation film (in-plane retardation value = 130 to 140 nm) manufactured by stretching polycarbonate was used. Table 1 shows the angle θ of the in-plane slow axis m with respect to the transmission axis n of the polarizing plate 3 (the retardation angle θ of the retardation film: plus (+) for clockwise and minus (-) for counterclockwise). It is described in Table 2.

  The optical rotatory layer 2 is composed of 100 parts by weight of a polymerizable liquid crystal compound (LC242 manufactured by BASF), 0.15 to 1 part by weight of a chiral agent (LC756 manufactured by BASF, right latent), and a polymerization initiator [Irgacure 907 manufactured by BASF Dextrorotatory)] 5 parts by weight dissolved in tetrahydrofuran, coated on a PET film by spin coating, dried, and then irradiated with UV light from a high-pressure mercury lamp to fix the orientation of the polymerizable liquid crystal compound. The material was transferred from a PET substrate with an adhesive and used. Furthermore, a TAC film was bonded for the purpose of protection.

  In this example, as shown in FIG. 2, the entire surface of the optical element 5 was bonded to the back surface of the glass plate 6 whose surface was treated with antiglare antireflection (AGAR) with an adhesive so as not to cause an air interface. In Examples 1 to 9, the stacking order was the polarizing plate 3, the optical rotatory layer 2, and the retardation layer 1 from the viewer side. In Comparative Example 1, a laminate including only the polarizing plate 3 and the retardation film (in-plane retardation value = 130 to 140 nm) was used. As the display unit 4, a display unit of an IPS liquid crystal display in which the transmission axis of the polarizing film bonded to the display surface from the time of shipment is the vertical direction was used. The transmittance was obtained from the luminance change in the front direction before and after mounting the optical element 5 of the present embodiment on the display unit 4. The reflectivity is the multi-objective film thickness measurement system F20 manufactured by Filmetrics. The optical element 5 of this example is placed on the mirror 7, and the reflectivity (@ 550 nm) of the normal incidence is the light projecting part / light receiving part 8 It measured using.

  In the determination of optical characteristics, the transmittance was determined to be a practical level if it was 50% or more, and determined to be not a practical level if the transmittance was less than 50%. The reflectance was determined to be a practical level if it was 10% or less, and determined to be not a practical level if the transmittance exceeded 10%. In Tables 1 and 2, both are marked with a mark of practical use and marked with x for others. Also, the shaded cells in the table indicate that the values described are not at a practical level.

  The effect of preventing the display from becoming difficult to see due to external light reflection (whiteout prevention effect) was confirmed by visually confirming the display unit 4 equipped with the optical element 5 in the vicinity of a window on a sunny day. The degree of effect is described as ◎ when the effect is excellent, ◯ when the effect is effective, Δ when the effect is weak, and × when there is no effect.

  As shown in FIG. 3, the windshield reflection preventing effect is arranged by tilting the glass plate 9 that looks like the windshield at an angle of 30 ° with respect to the horizontal direction, and the windshield (glass plate 9) when mounted on the vehicle, The arrangement of the display unit 4 and the optical element 5 of the present embodiment is simulated and reproduced in the dark room, and the reflected image Q when the display unit 4 is lit at the eye point of the driver in the left-hand drive vehicle is visually observed. Confirmed by The degree of effect is described as ◎ when the effect is excellent, ◯ when the effect is effective, Δ when the effect is weak, and × when there is no effect.

  When comparing the results of Example 1 to Example 9 and the result of Comparative Example 1 with Tables 1 and 2, by using the configuration of the present embodiment, the reflectance of outside light is maintained while maintaining the transmittance. It was confirmed that it can be reduced. As a result, it was confirmed that a whiteout prevention effect was obtained, and further a windshield reflection prevention effect was also obtained. In addition, although the comparative example 1 was able to acquire the whiteout prevention effect, the transmittance | permeability was low and was not able to endure practical use.

  In these examples, when the back surface of the optical element 5 is further anti-reflective treated (TAC film surface is subjected to the above LR treatment) and the entire surface is bonded with an adhesive so that there is no air interface, the whiteout prevention effect is further enhanced. It was confirmed. Furthermore, the influence of the mounting angle (that is, the influence of the transmission axis n of the polarizing plate 3 of the optical element 5) was examined using the optical element 5 having a retardation film bonding angle of 35 ° in Example 6. Assuming observation from the driver's eyepoint in a left-hand drive vehicle, changing the mounting angle of the optical element 5 will result in + 15 ° to 0 ° with respect to the horizontal direction (0 °) perpendicular to the vertical direction. It was confirmed that the reflection preventing effect was excellent without a significant decrease in transmittance. Beyond this range, it was confirmed that the effect of preventing reflection gradually decreased.

Example 10
The optical element 5 of this embodiment was mounted on a display unit of a TN liquid crystal display in which the transmission axis of the polarizing film on the display surface was 135 ° with respect to the horizontal direction, and the characteristics were confirmed. An optical element polarizing plate using a transmission axis n of the polarizing plate 3 as a vertical direction, a film having an optical rotation angle of 56.5 ° as the optical rotatory layer 2, and a retardation film having an in-plane retardation value of 140 nm as the retardation layer 1. The slow axis m of the retardation film was set to + 15 ° with respect to the transmission axis n. In the optical element 5, the stacking order was the polarizing plate 3, the optical rotatory layer 2, and the retardation layer 1 from the viewer side. The transmittance of the optical element 5 in this configuration was 59.3%, and the external light reflectance was 8.3%. In the vicinity of the window on a clear day, the display unit 4 equipped with the optical element 5 was visually confirmed to confirm that it also had a whiteout prevention effect. In addition, with regard to the effect of preventing windshield reflection, a decrease in luminance was confirmed in the reflected image before and after installation.

Example 11
In the same manner as in Examples 1 to 9, the display unit 4 was mounted with the optical element 5 of this embodiment on an IPS liquid crystal display in which the transmission axis of the polarizing film glass was vertical, and the characteristics were confirmed. With the transmission axis n of the polarizing plate 3 as the vertical direction, as the optical rotation layer 2, 100 parts by weight of a polymerizable liquid crystal compound (LC242 manufactured by BASF), 4 parts by weight of a chiral agent [manufactured by Merck, S811 (left-handed)], and 5 parts by weight of a polymerization initiator (BASF Irgacure 907) is dissolved in tetrahydrofuran, applied onto a PET film by spin coating, dried, and then irradiated with UV light from a high-pressure mercury lamp to align the polymerizable liquid crystal compound. What was fixed and produced was transferred from a PET film with an adhesive and used. This optical rotatory layer 2 is a film having an optical rotation angle of 73.0 °, and a retardation film having an in-plane retardation value of 140 nm is used as the retardation layer 1, and with respect to the transmission axis n of the optical element polarizing plate, The angle of the slow axis m of the retardation film was −35 °. In the optical element 5, the stacking order was the polarizing plate 3, the optical rotatory layer 2, and the retardation layer 1 from the viewer side. The transmittance of the optical element 5 in this configuration was 60.5%, and the external light reflectance was 6.3%. In the vicinity of the window on a clear day, the display unit 4 equipped with the optical element 5 was visually confirmed to confirm that it also had a whiteout prevention effect. In addition, when observed from the driver's eyepoint in a right-hand drive vehicle, the effect of preventing windshield reflection was confirmed.

  As described above, according to this example, it was confirmed that the reflectance of external light can be reduced while maintaining the transmittance. As a result, it was confirmed that a whiteout prevention effect was obtained, and further a windshield reflection prevention effect was also obtained. Therefore, according to the optical element of the present invention, in an in-vehicle display device arranged on a dashboard, the reflected light in the viewer direction is reduced with respect to the external light with a simple configuration, and the external light Visibility degradation due to reflection can be suppressed. Furthermore, the effect of preventing windshield reflection can be exhibited with a simple configuration.

  The present invention is not limited to the above-described embodiment, and various additions, changes, or deletions can be made without departing from the gist of the present invention. For example, depending on the difference between the right or left handle, the mounting position on the vehicle, the position of the windshield, the position of the eye point, etc., the bonding order and bonding angle can be changed as appropriate, and those changes have been made. Are also included in the present invention.

1: Retardation layer 2: Optical rotation layer 3: Polarizing plate 4: Display device 5: Optical element 6: Glass plate whose surface has been subjected to AGAR 7: Mirror 8: Light projecting unit / light receiving unit 9: Glass plate

Claims (8)

A transmissive optical element mounted on a display unit,
A polarizing plate is provided on the side to be visually recognized,
An optical element comprising a retardation layer and an optical rotation layer having optical activity between the polarizing plate and the display unit.   2. The optical element according to claim 1, wherein an in-plane retardation of the retardation layer is 90 nm to 185 nm with respect to light having a wavelength of 550 nm.   The optical element according to claim 1 or 2, wherein an optical rotation angle of the optical rotatory layer is ± 20 ° to ± 80 °.   The optical element according to any one of claims 1 to 3, wherein a transmission axis of the polarizing plate is set within a range of ± 15 degrees with respect to a vertical direction.   5. The optical element according to claim 1, wherein the polarizing plate, the retardation layer, and the optical rotatory layer are laminated in this order from the visually recognized side, and the transmission axis of the polarizing plate. And an angle between the slow axis of the retardation layer and the retardation axis is set in a range of ± 20 degrees to ± 70 degrees.   The optical element according to any one of claims 1 to 5, wherein the side to be viewed, the side facing the side to be viewed, or the side facing the side to be viewed and the viewer side are disposed. An optical element comprising an anti-reflection layer formed on at least one of anti-glare treatment, anti-reflection treatment, and low reflection treatment on both sides. An in-vehicle display device, wherein the optical element according to any one of claims 1 to 6 is mounted.   8. The in-vehicle display device according to claim 7, further comprising an operation touch panel device between the display unit and the optical element.

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