Liquid crystal element and head-mounted display

Abstract

To provide a liquid crystal element and a head mount display, in which polarization modulation and polarization non-modulation can be switched in a wide band range and a wide viewing angle and the orientation stability is excellent.SOLUTION: A liquid crystal element includes a first substrate, a first horizontal orientation film of weak anchoring, a liquid crystal layer containing a two-frequency driving liquid crystal molecule, a second horizontal orientation film of weak anchoring, and a second substrate in this order. At least one of the first substrate and the second substrate includes an interdigital electrode for generating an electric field to the liquid crystal layer. The two-frequency driving liquid crystal molecule is twist-oriented between the first substrate and the second substrate in a voltage applied state and a voltage non-applied state. The twisting direction in the voltage applied state and the twisting direction in the voltage non-applied state are the same. The orientation direction of the two-frequency driving liquid crystal molecule at the center of the liquid crystal layer in a thickness direction is orthogonal or parallel to an extending direction of the interdigital electrode.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The following disclosure relates to a liquid crystal element and a head-mounted display.

Background Art

[0002] In recent years, a variable focus optical system combining a Pancharatnam Berry (PB) lens and a liquid crystal element such as a switchable half-wave plate (sHWP) has been proposed for head-mounted displays and the like. The sHWP is a device capable of switching the polarization states of left and right circular polarizations and is realized by liquid crystal.

[0003] As a technology related to a variable focus optical system, for example, Patent Document 1 discloses a display device including a waveguide and a broadband adaptive lens assembly, wherein the waveguide is configured to guide light in a lateral direction parallel to an output surface of the waveguide, and further configured to externally couple the guided light through the output surface, and the broadband adaptive lens assembly is configured to internally couple and diffract the externally coupled light from the waveguide therethrough.

[0004] Patent Document 2 discloses a variable focus block including an sHWP and a plurality of liquid crystal lenses.

[0005] Patent Document 3 discloses an optical element including a liquid crystal cell having a first substrate, a liquid crystal layer, and a second substrate, and a quarter-wave plate. The liquid crystal layer contains liquid crystal molecules having a twisted alignment, the liquid crystal cell has electrodes, and the electrodes are arranged such that a first state and a second state can be switched by applying a voltage to the liquid crystal layer. The switching between the first state and the second state controls the polarization state of light incident on the liquid crystal cell. When circularly polarized light is incident on the liquid crystal cell, in the first state, the circularly polarized light is converted into first linearly polarized light, and in the second state, the circularly polarized light is converted into second linearly polarized light. When linearly polarized light is incident on the liquid crystal cell, in the first state, the linearly polarized light is converted into first circularly polarized light, and in the second state, the linearly polarized light is converted into second circularly polarized light.

[0006] Patent Document 4 discloses an optical element including a first liquid crystal cell having first liquid crystal molecules and a first electrode, and a second liquid crystal cell having second liquid crystal molecules and a second electrode. The first electrode and the second electrode are arranged such that a first state in which the second liquid crystal molecules have a twisted alignment and the first liquid crystal molecules have a perpendicular alignment, and a second state in which the first liquid crystal molecules have a twisted alignment and the second liquid crystal molecules have a perpendicular alignment can be switched. The azimuth angles of the alignment directions of the second liquid crystal molecules on the third substrate side and the fourth substrate side in the first state are respectively angles obtained by rotating the azimuth angles of the alignment directions of the first liquid crystal molecules on the first substrate side and the second substrate side in the second state in the same direction by 1 / 4 turn.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the above Patent Documents 1 to 2, there is a problem that it is difficult to realize a device structure capable of switching between polarization modulation for converting the polarization states of left and right circularly polarized lights and non-polarization modulation for not converting the polarization states of left and right circularly polarized lights over a wide band and a wide viewing angle. In the above Patent Document 3, there is a problem that it is difficult to realize a device structure excellent in alignment stability. In the above Patent Document 4, it is possible to realize a highly reliable device by laminating a twisted-aligned liquid crystal layer, but there are problems that the thickness becomes thick or the weight becomes heavy.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid crystal element and a head-mounted display capable of switching polarization modulation and non-polarization modulation over a wide band and a wide viewing angle and having excellent alignment stability.

Means for Solving the Problems

[0010] (1) One embodiment of the present invention sequentially includes a first substrate, a first weakly anchoring horizontal alignment film, a liquid crystal layer containing two-frequency driving liquid crystal molecules, a second weakly anchoring horizontal alignment film, and a second substrate. At least one of the first substrate and the second substrate has a comb electrode for generating an electric field in the liquid crystal layer. The two-frequency driving liquid crystal molecules are twisted and aligned between the first substrate and the second substrate in a voltage-applied state and a voltage-non-applied state, and the twist direction in the voltage-applied state and the twist direction in the voltage-non-applied state are the same. The alignment direction of the two-frequency driving liquid crystal molecules located at the center in the thickness direction of the liquid crystal layer is orthogonal or parallel to the extending direction of the comb electrode.

[0011] (2) Further, in a certain embodiment of the present invention, in addition to the configuration of (1) above, the first weakly anchoring horizontal alignment film has an azimuthal anchoring energy of 1×10-4 J / m 2 A liquid crystal element having less than...

[0012] (3) Further, in a certain embodiment of the present invention, in addition to the configuration of (1) or (2) above, the horizontal alignment film of the first weak anchoring contains a polymer having at least one of a group represented by the following structural formula (P1) and a group represented by the following structural formula (P2). A liquid crystal element.

[0013]

Chemical formula

[0014]

Chemical formula

[0015] (4) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), or (3) above, the horizontal alignment film of the second weak anchoring has an azimuthal anchoring energy of 1×10 -4 J / m 2 less than. A liquid crystal element.

[0016] (5) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), or (4) above, the horizontal alignment film of the second weak anchoring contains a polymer having at least one of a group represented by the following structural formula (P1) and a group represented by the following structural formula (P2). A liquid crystal element.

[0017]

Chemical formula

[0018] [Chemistry] (In the above structural formula, X has at least one group among an ether group, an ester group, and an amide group, and R 1 , R 2 , R 3 and R 4 each independently represent a hydrocarbon group, and Y is a carbon atom or a silicon atom.)

[0019] (6) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), or (5) above, the first weakly anchoring horizontal alignment film and the second weakly anchoring horizontal alignment film do not have uniaxial orientation, a liquid crystal element.

[0020] (7) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), or (6) above, the first weakly anchoring horizontal alignment film and the second weakly anchoring horizontal alignment film have an in-plane retardation of less than 1 nm, a liquid crystal element.

[0021] (8) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), or (7) above, in a state without applied voltage, the alignment direction of the two-frequency driving liquid crystal molecules located at the center in the thickness direction of the liquid crystal layer is orthogonal to the stretching direction of the comb-shaped electrodes, a liquid crystal element.

[0022] (9) Further, in a certain embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), or (8) above, the comb-shaped electrodes are provided only on one of the first substrate and the second substrate, a liquid crystal element.

[0023] (10) Further, in an embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), (7), (8), or (9) above, the comb-shaped electrode has a comb-shaped electrode on the first substrate side provided on the first substrate and a comb-shaped electrode on the second substrate side provided on the second substrate, and the extending direction of the comb-shaped electrode on the first substrate side is parallel to the extending direction of the comb-shaped electrode on the second substrate side. Liquid crystal element.

[0024] (11) Further, in an embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), (7), (8), (9), or (10) above, the ratio of the electrode width to the slit width of the comb-shaped electrode (electrode width: slit width) is 1:2 to 1:6. Liquid crystal element.

[0025] (12) Further, in an embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), or (11) above, the ratio of the thickness of the liquid crystal layer to the slit width of the comb-shaped electrode (thickness of the liquid crystal layer: slit width) is 1:2.5 to 1:10. Liquid crystal element.

[0026] (13) Further, in an embodiment of the present invention, in addition to the configurations of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), or (12) above, further, at least one side of the side of the first substrate opposite to the liquid crystal layer and the side of the second substrate opposite to the liquid crystal layer is provided with a retardation film. Liquid crystal element.

[0027] (14) Further, in an embodiment of the present invention, in addition to the configuration of (13) above, the retardation film has a first quarter-wave film and a second quarter-wave film in order from the side close to the liquid crystal layer. Liquid crystal element.

[0028] (15) Further, in another embodiment of the present invention, in addition to the configurations of the above (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13) or (14), at least one of the horizontal alignment films of the first weak anchoring and the horizontal alignment film of the second weak anchoring is in contact with the comb-shaped electrode and contains at least two types of polymers having different refractive indices from each other. The polymer having the smallest refractive index among the at least two types of polymers is in contact with the liquid crystal layer. A liquid crystal element.

[0029] (16) Further, in another embodiment of the present invention, in addition to the configurations of the above (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14) or (15), the ratio of the azimuth anchoring energy of the horizontal alignment film of the second weak anchoring to the azimuth anchoring energy of the horizontal alignment film of the first weak anchoring is 10 or less. A liquid crystal element.

[0030] (17) Further, in another embodiment of the present invention, in addition to the configurations of the above (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15) or (16), further, the first substrate or the second substrate includes a curved flexible printed circuit board, and the comb-shaped electrode is provided only on the substrate located in the bending direction of the flexible printed circuit board among the first substrate and the second substrate. A liquid crystal element.

[0031] (18) Further, another embodiment of the present invention is a head-mounted display including the liquid crystal element described in the above (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16) or (17).

Advantages of the Invention

[0032] According to the present invention, it is possible to provide a liquid crystal element and a head-mounted display that can switch between polarization modulation and non-polarization modulation over a wide band and a wide viewing angle and have excellent alignment stability.

Brief Description of the Drawings

[0033]

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Mode for Carrying Out the Invention

[0034] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the contents described in the following embodiments, and design changes can be appropriately made within the scope that satisfies the configuration of the present invention. In the following description, the same reference numerals are commonly used for the same parts or parts having the same functions among different drawings as appropriate, and the repeated description thereof is omitted as appropriate. Each aspect of the present invention may be appropriately combined without departing from the gist of the present invention.

[0035] (Definition of Terms) In this specification, the orientation means the direction when the target direction is projected onto the substrate surface on the emission side of the liquid crystal element, and is expressed by the angle (orientation angle) formed with the reference orientation. Here, the reference orientation (0°) is set to the direction when the alignment direction of the liquid crystal molecules on the first substrate side in the first state is projected onto the substrate surface on the emission side of the liquid crystal element. That is, the orientation angle of the alignment direction of the liquid crystal molecules on the first substrate side in the first state is set to 0°. The orientation angle is a positive angle counterclockwise from the reference orientation and a negative angle clockwise from the reference orientation. Both counterclockwise and clockwise represent the rotation direction when the liquid crystal element is viewed from the emission side. Also, the orientation angle represents a value measured in a plan view of the liquid crystal element from the emission side.

[0036] In this specification, when two straight lines (including axes, directions, and orientations) are orthogonal to each other, it means they are orthogonal when the liquid crystal element is viewed in a plan view from the emission side. Also, when one of the two straight lines is provided obliquely with respect to the other straight line, it means that one straight line is provided obliquely with respect to the other straight line when the liquid crystal element is viewed in a plan view from the emission side. Further, the angle formed by two straight lines means the angle formed by one straight line and the other straight line in the state where the liquid crystal element is viewed in a plan view from the emission side.

[0037] In this specification, when two straight lines (including axes, directions, and orientations) are orthogonal, it means that the angle formed by the two is 90° ± 5°, preferably 90° ± 1°, more preferably 90° ± 0.5°, and particularly preferably 90° (completely orthogonal). When two straight lines are parallel, it means that the angle formed by the two is 0° ± 3°, preferably 0° ± 1°, more preferably 0° ± 0.5°, and particularly preferably 0° (completely parallel).

[0038] Refractive indices (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane, and "nz" is the refractive index in the thickness direction. Unless otherwise specified, the refractive index refers to the value for light at 23°C and a wavelength of 550 nm.

[0039] In-plane retardation (Re) The in-plane retardation (Re) refers to the in-plane retardation of the layer (film) at 23°C and a wavelength of 550 nm unless otherwise specified. Re is obtained by Re = (nx - ny) × d, where d (nm) is the thickness of the layer (film). In this specification, unless otherwise specified, "retardation" refers to the in-plane retardation.

[0040] Retardation in the thickness direction (Rth) The retardation in the thickness direction (Rth) refers to the retardation in the thickness direction of the layer (film) at 23°C and, unless otherwise specified, at a wavelength of 550 nm. When the thickness of the layer (film) is d (nm), Rth is obtained by Rth = (nz - (nx + ny) / 2) × d. In this specification, the retardation in the thickness direction is also referred to as the "thickness retardation".

[0041] Note that in this specification, the measurement wavelength of optical parameters such as the main refractive index and retardation is 550 nm unless otherwise specified.

[0042] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the contents described in the following embodiments, and design changes can be appropriately made within the scope that satisfies the configuration of the present invention.

[0043] (Embodiment 1) FIG. 1 is a schematic cross-sectional view of a liquid crystal element according to Embodiment 1. FIG. 2 is a perspective schematic view of the liquid crystal element according to Embodiment 1. FIG. 3 is a schematic view for explaining the alignment of liquid crystal molecules in the first state and the second state of the liquid crystal element according to Embodiment 1. FIG. 4 is a view showing the axial orientation of the liquid crystal element according to Embodiment 1.

[0044] The liquid crystal element 10 of the present embodiment shown in FIGS. 1 to 4 includes a first substrate 100, a first weakly anchoring horizontal alignment film 411, a liquid crystal layer 300 containing two-frequency driving liquid crystal molecules 310, a second weakly anchoring horizontal alignment film 421, and a second substrate 200 in this order. The liquid crystal element 10 has a comb electrode 11 for generating an electric field (preferably, for generating a transverse electric field) for the liquid crystal layer 300 on at least one of the first substrate 100 and the second substrate 200. The two-frequency driving liquid crystal molecules 310 are twisted and aligned between the first substrate 100 and the second substrate 200 in both the voltage-applied state and the voltage-non-applied state, and the twist direction in the voltage-applied state is the same as the twist direction in the voltage-non-applied state. The alignment direction of the two-frequency driving liquid crystal molecules 310 located at the center in the thickness direction of the liquid crystal layer 300 is orthogonal or parallel to the extending direction 11A of the comb electrode 11. By adopting such a mode, the alignment stability can be improved.

[0045] The liquid crystal element 10 of this embodiment is a phase modulation element capable of switching between polarization modulation that converts the polarization states of left and right circularly polarized lights and polarization non-modulation that does not convert the polarization states of left and right circularly polarized lights. Here, it is preferable that the phase modulation element has a high degree of circular polarization in both the modulation state and the non-modulation state. When a strongly anchoring alignment film is disposed as an alignment film on one of the interfaces between the first substrate and the liquid crystal layer and between the second substrate and the liquid crystal layer, the initial alignment is stabilized because the liquid crystal molecules are likely to align along the strongly anchoring alignment film. However, due to the alignment restricting force of the strongly anchoring alignment film, the movement of the liquid crystal molecules becomes difficult. For example, the polarization modulation characteristics in the modulation state are good, but the polarization modulation characteristics in the non-modulation state may deteriorate. Depending on the design, the polarization modulation characteristics in the non-modulation state may be good, but the polarization modulation characteristics in the modulation state may deteriorate. That is, it is difficult to achieve good polarization modulation characteristics in both the modulation state and the non-modulation state.

[0046] To solve this problem, it is conceivable to use a weakly anchoring alignment film on both the first substrate and the second substrate. However, since the weakly anchoring alignment film has a weak alignment restricting force, it is generally difficult to improve the alignment stability.

[0047] The inventors have hitherto considered that the effect of the comb-shaped electrodes provided on the substrates acts on the vicinity of the "substrate interface", and thus have considered that it is good for the liquid crystal molecules located near the interfaces between the first substrate and the second substrate and the liquid crystal layer to align parallel or perpendicular to the extending direction of the comb-shaped electrodes. However, in the case of this embodiment in which both substrates are provided with weakly anchoring alignment films, it has been found that the effect of the comb-shaped electrodes can act on the liquid crystal molecules located near the center (bulk) of the liquid crystal layer rather than the liquid crystal molecules located near the interfaces.

[0048] Therefore, in the present embodiment, a first weakly anchoring horizontal alignment film 411 and a second weakly anchoring horizontal alignment film 421 are respectively disposed between the first substrate 100 and the liquid crystal layer 300, and between the second substrate 200 and the liquid crystal layer 300. Further, by using the dual-frequency driven liquid crystal molecules 310 and arranging the alignment direction of the dual-frequency driven liquid crystal molecules 310 located at the center in the thickness direction of the liquid crystal layer 300 to be orthogonal or parallel to the extending direction 11A of the comb-shaped electrode 11, the alignment of the dual-frequency driven liquid crystal molecules 310 (also referred to as bulk dual-frequency driven liquid crystal molecules 310) located in the regions away from the interfaces between the first substrate 100 and the liquid crystal layer 300 and between the second substrate 200 and the liquid crystal layer 300 is stabilized, thereby realizing good alignment stability. Hereinafter, the liquid crystal element 10 of the present embodiment will be described in detail.

[0049] As shown in FIGS. 1 and 2, the first substrate 100 includes a first support substrate 110 and a comb-shaped electrode 11 in this order toward the liquid crystal layer 300 side. The second substrate 200 includes a second support substrate 210 and does not include a comb-shaped electrode. The structure composed of the members from the first substrate 100 to the second substrate 200 is also referred to as a liquid crystal cell 11C. That is, the first substrate 100, the first weakly anchoring horizontal alignment film 411, the liquid crystal layer 300, the second weakly anchoring horizontal alignment film 421, and the second substrate 200 constitute the liquid crystal cell 11C.

[0050] The comb-shaped electrode 11 is arranged such that the voltage applied to the liquid crystal layer 300 can switch between a first state in which the dual-frequency driven liquid crystal molecules 311 on the first substrate 100 side are arranged in the first alignment direction 311A and a second state in which the dual-frequency driven liquid crystal molecules 311 on the first substrate 100 side are arranged in a second alignment direction 311B orthogonal to the first alignment direction 311A in a plan view.

[0051] The comb-shaped electrode 11 has a structure in which the linear electrode portions 11E and the slit portions 11S are alternately and repeatedly arranged. The electrode width of the comb-shaped electrode 11 means the width per one linear electrode portion 11E. The slit width of the comb-shaped electrode 11 means the width per one slit portion 11S. The pitch of the comb-shaped electrode 11 means the sum of the widths of a set of the linear electrode portion 11E and the slit portion 11S. The extending direction 11A of the comb-shaped electrode 11 means the direction in which the linear electrode portion 11E extends. Here, the comb-shaped electrode has a trunk electrode portion extending in a first direction and a plurality of linear electrode portions extending from the trunk electrode portion in a second direction different from the first direction. In FIGS. 1 to 4 and the like, the structure of the trunk electrode portion of the comb-shaped electrode is omitted, and only the linear electrode portions are shown.

[0052] In this embodiment, as the comb-shaped electrode 11, an IPS (In-Plane Switching) electrode in which a strip-shaped common electrode and a strip-shaped pixel electrode are alternately arranged is used, but the structure of the comb-shaped electrode 11 is not limited to this. For example, an FFS (Fringe Field Switching) electrode can also be preferably used. The FFS electrode includes, for example, a pixel electrode provided with slits via an insulating film on a planar common electrode. Further, the FFS electrode may include a common electrode provided with slits via an insulating film on a planar pixel electrode formed so as to occupy each pixel region. The comb-shaped electrode 11 of this embodiment is preferably an IPS electrode. By adopting such an aspect, the transmittance and the circular polarization degree can be improved.

[0053] In this specification, a voltage application state in which a voltage equal to or higher than a threshold value is applied between a pair of common electrodes and a pixel electrode is also simply referred to as "voltage application state" or "when voltage is applied", and a voltage non-application state in which no voltage is applied between a pair of common electrodes and a pixel electrode (including the case where a voltage lower than the threshold value is applied) is also simply referred to as "voltage non-application state" or "when voltage is not applied".

[0054] In this embodiment, the comb-shaped electrode 11 is provided on only one of the first substrate 100 and the second substrate 200. By adopting such a mode, the liquid crystal element 10 can have a simpler structure, and the productivity can be improved. In addition, if the comb-shaped electrodes 11 are arranged on both the first substrate 100 and the second substrate 200, moiré is likely to occur. However, in this embodiment, there is no such concern, and the in-plane uniformity of the optical characteristics can be improved.

[0055] The ratio of the electrode width to the slit width of the comb-shaped electrode 11 (electrode width: slit width) is preferably 1:2 to 1:6. By adopting such a mode, the alignment uniformity can be further improved. As a result, the degree of polarization of the emitted light can be improved. The ratio of the electrode width to the slit width of the comb-shaped electrode 11 (electrode width: slit width) is more preferably 1:2.5 to 1:5, and the ratio of the electrode width to the slit width of the comb-shaped electrode 11 (electrode width: slit width) is even more preferably 1:3 to 1:4.

[0056] The ratio of the thickness of the liquid crystal layer 300 to the slit width of the comb-shaped electrode 11 (thickness of the liquid crystal layer: slit width) is preferably 1:2.5 to 1:10. By adopting such a mode, the alignment uniformity can be further improved. As a result, the degree of polarization of the emitted light can be improved. The ratio of the thickness of the liquid crystal layer 300 to the slit width of the comb-shaped electrode 11 (thickness of the liquid crystal layer: slit width) is more preferably 1:3 to 1:8, and the ratio of the thickness of the liquid crystal layer 300 to the slit width of the comb-shaped electrode 11 (thickness of the liquid crystal layer: slit width) is even more preferably 1:4 to 1:6.

[0057] The comb-shaped electrode 11 has a pixel electrode which is a comb-shaped electrode and a common electrode which is a comb-shaped electrode. The pixel electrode and the common electrode can be formed, for example, by forming a single layer or a plurality of layers of a transparent conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), tin oxide (SnO), or an alloy thereof by a sputtering method or the like, and then performing patterning using a photolithography method.

[0058] The azimuth angle of the extending direction 11A of the comb-shaped electrode 11 is preferably, for example, 115° or more and 155° or less. By adopting such an aspect, a modulated state can be realized when no voltage is applied or when a voltage of a low frequency is applied, and an unmodulated state can be realized when a voltage of a high frequency is applied.

[0059] Also, the azimuth angle of the extending direction 11A of the comb-shaped electrode 11 is preferably, for example, 25° or more and 65° or less. By adopting such an aspect, an unmodulated state can be realized when no voltage is applied or when a voltage of a low frequency is applied, and a modulated state can be realized when a voltage of a high frequency is applied.

[0060] As shown in FIGS. 3 and 4, the comb-shaped electrode 11 is arranged so that the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side can be switched between a first state in which the two-frequency driving liquid crystal molecules 311 are arranged in a first alignment direction 311A and a second state in which the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side are arranged in a second alignment direction 311B orthogonal to the first alignment direction 311A in a plan view by applying a voltage to the liquid crystal layer 300.

[0061] The switching between the first state and the second state controls the polarization state of the light incident on the liquid crystal cell 11C. When circularly polarized light is incident on the liquid crystal cell 11C, in the first state, the circularly polarized light is converted into first linearly polarized light, and in the second state, the circularly polarized light is converted into second linearly polarized light having a polarization direction orthogonal to the polarization direction of the first linearly polarized light in a plan view. When linearly polarized light is incident on the liquid crystal cell 11C, in the first state, the linearly polarized light is converted into first circularly polarized light, and in the second state, the linearly polarized light is converted into second circularly polarized light rotating in a direction opposite to the rotation direction of the first circularly polarized light. By adopting such an aspect, it is possible to switch, in a wide band, between a state in which the circularly polarized light incident on the liquid crystal element 10 is emitted without being modulated while suppressing the thickness of the liquid crystal element 10 and a state in which the circularly polarized light incident on the liquid crystal element 10 is modulated and then emitted. That is, it is possible to realize a liquid crystal element 10 that can switch between polarization modulation and non-polarization modulation in a wide band and can be thinned.

[0062] In the liquid crystal element 10 of the present embodiment including the liquid crystal cell 11C and the retardation film 500 described later, the first state is a polarization modulation state that converts the polarization states of left and right circularly polarized lights, and the second state is a polarization non-modulation state that does not convert the polarization states of left and right circularly polarized lights. Here, the alignment direction of the two-frequency driving liquid crystal molecules on the first substrate side refers to the alignment direction of the two-frequency driving liquid crystal molecules located at the interface on the first substrate side of the liquid crystal layer. Similarly, the alignment direction of the two-frequency driving liquid crystal molecules on the second substrate side refers to the alignment direction of the two-frequency driving liquid crystal molecules located at the interface on the second substrate side of the liquid crystal layer.

[0063] The alignment direction of the two-frequency driving liquid crystal molecules on the first substrate side and the alignment direction of the two-frequency driving liquid crystal molecules on the second substrate side can be measured from the Mueller matrix output by measuring the liquid crystal cell with Axoscan (manufactured by Axometrics). Also, the alignment direction of the two-frequency driving liquid crystal molecules on the first substrate side and the alignment direction of the two-frequency driving liquid crystal molecules on the second substrate side can be obtained by software that fits the cell thickness and twist angle of the liquid crystal within Axoscan.

[0064] The liquid crystal layer 300 contains two-frequency driving liquid crystal molecules 310. By adopting such a mode, two liquid crystal alignment states (that is, the modulation state and the non-modulation state) can be switched by the comb electrodes 11 provided only on one substrate. Further, since the liquid crystal layer 300 contains two-frequency driving liquid crystal molecules 310, even when the liquid crystal layer 300 is sandwiched between two weakly anchoring alignment films (in the present embodiment, the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421), the alignment stability can be enhanced by performing a voltage application and realignment process. Note that when ordinary liquid crystal molecules are used, alignment stabilization itself is possible, but the modulation state and the non-modulation state cannot be switched only by the comb electrodes provided on one substrate.

[0065] The two-frequency driven liquid crystal molecules 310 exhibit the behavior of positive-type liquid crystal molecules with positive dielectric anisotropy (Δε) when a low-frequency voltage is applied, and exhibit the behavior of negative-type liquid crystal molecules with negative Δε when a high-frequency voltage is applied. Note that a single compound may exhibit the above behavior, or a mixture of multiple compounds may exhibit the above behavior. In this specification, in either case, it is referred to as two-frequency driven liquid crystal molecules.

[0066] When using two-frequency liquid crystals, even if comb electrodes with different angles are not provided on each of the upper and lower substrates (the first substrate 100 and the second substrate 200), when low-frequency driving is performed on a single comb electrode, the liquid crystal molecules are oriented in a direction perpendicular to the stretching direction of the comb electrode, and when high-frequency driving is performed, the liquid crystal molecules are oriented in the stretching direction of the comb electrode. Therefore, the electrode configuration can be simplified. Δε is represented by the following (Equation L). Δε = (dielectric constant in the long axis direction of the liquid crystal molecule) - (dielectric constant in the short axis direction of the liquid crystal molecule) (Equation L)

[0067] In this embodiment, the low frequency is, for example, 1 Hz or more and 1 kHz or less, and the high frequency is 10 kHz or more and 1 MHz or less. Note that the frequency at which the positive and negative of Δε are reversed is called the crossover frequency, and can be appropriately adjusted according to the molecular structure of the liquid crystal material, the mixing ratio of the mixture, and the like.

[0068] The two-frequency driven liquid crystal molecules 310 are twisted and oriented between the first substrate 100 and the second substrate 200. In each of the first state and the second state, the two-frequency driven liquid crystal molecules 310 are twisted and oriented from the first substrate 100 side to the second substrate 200 side. The direction in which the two-frequency driven liquid crystal molecules 310 are twisted in the first state is the same as the direction in which the two-frequency driven liquid crystal molecules 310 are twisted in the second state. By adopting such a mode, good polarization modulation characteristics can be obtained in both of the two states (the non-modulated state and the modulated state).

[0069] The twist direction of the dual-frequency driving liquid crystal molecules 310 in the voltage-applied state is the same as that in the voltage-unapplied state. For example, when the twist direction in the voltage-applied state is clockwise, the twist direction in the voltage-unapplied state is also clockwise; when the twist direction in the voltage-applied state is counterclockwise, the twist direction in the voltage-unapplied state is also counterclockwise.

[0070] The twisted alignment of the dual-frequency driving liquid crystal molecules 310 can be realized, for example, by adding a chiral agent to the liquid crystal material. The chiral agent is not particularly limited, and conventionally known ones can be used. As the chiral agent, for example, S-811 (manufactured by Merck & Co., Inc.) etc. can be used.

[0071] In plan view, the angle formed by the alignment direction (first alignment direction) 311A of the dual-frequency driving liquid crystal molecules 311 on the first substrate 100 side in the first state and the alignment direction 312A of the dual-frequency driving liquid crystal molecules 312 on the second substrate 200 side is preferably 57° or more and 82° or less, more preferably 63° or more and 75° or less, and still more preferably 66° or more and 72° or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched in a wider band. Hereinafter, in plan view, the angle formed by the alignment direction of the dual-frequency driving liquid crystal molecules on the first substrate side and the alignment direction of the dual-frequency driving liquid crystal molecules on the second substrate side is also referred to as the twist angle.

[0072] In plan view, the angle formed by the alignment direction (second alignment direction) 311B of the dual-frequency driving liquid crystal molecules 311 on the first substrate 100 side in the second state and the alignment direction 312B of the dual-frequency driving liquid crystal molecules 312 on the second substrate 200 side is preferably 57° or more and 82° or less, more preferably 63° or more and 75° or less, and still more preferably 66° or more and 72° or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be effectively switched in a wider band. The twist angle in the first state and the twist angle in the second state may be the same or different, but it is preferably the same.

[0073] Also, the twist angle when no voltage is applied is preferably 67° or more and 92° or less, more preferably 73° or more and 85° or less, and even more preferably 76° or more and 82° or less. Since the twist angle decreases with the application of voltage, if the twist angle when no voltage is applied is set as described above, both the twist angles in the first state and the second state can be within the above-mentioned suitable ranges, so that polarization modulation and non-polarization modulation can be effectively switched in a wide band.

[0074] The alignment direction of the two-frequency driving liquid crystal molecules 310 located at the center in the thickness direction of the liquid crystal layer 300 is also referred to as the liquid crystal average alignment direction. The liquid crystal average alignment direction is arranged in the middle between the alignment direction of the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side and the alignment direction of the two-frequency driving liquid crystal molecules 312 on the second substrate 200 side.

[0075] As shown in FIGS. 3 and 4, when no voltage is applied to the comb-shaped electrode 11 (also referred to as voltage-off), the alignment direction (liquid crystal average alignment direction) 310A of the two-frequency driving liquid crystal molecules 310 located at the center in the thickness direction of the liquid crystal layer 300 is perpendicular to the extending direction 11A of the comb-shaped electrode 11. For example, when manufacturing the liquid crystal element 10, when performing liquid crystal realignment while applying a low-frequency voltage, in the voltage-off state, the alignment direction of the two-frequency driving liquid crystal molecules 310 located at the center in the thickness direction of the liquid crystal layer 300 is perpendicular to the extending direction 11A of the comb-shaped electrode 11. The voltage applied at this time needs to be less than the crossover frequency of the two-frequency driving liquid crystal molecules 310. For example, it is preferably 1 Hz or more and 1 kHz or less, and 1 V or more and 10 V or less. By performing this process, a uniform alignment in a state where the liquid crystal average alignment direction 310A of the two-frequency driving liquid crystal molecules 310 when no voltage is applied to the comb-shaped electrode 11 is perpendicular to the extending direction 11A of the comb-shaped electrode 11 can be obtained.

[0076] In this embodiment, attention is paid to the relationship between the average liquid crystal alignment direction 310A and the stretching direction 11A of the comb-shaped electrode 11, rather than the alignment directions of the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side and the two-frequency driving liquid crystal molecules 312 on the second substrate 200 side. This is because the two-frequency driving liquid crystal molecules 310 (also referred to as bulk two-frequency driving liquid crystal molecules) located in a region farther from the substrate are more susceptible to the influence of the stretching direction 11A (the direction of the electric field E) of the comb-shaped electrode 11 than the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side and the two-frequency driving liquid crystal molecules 312 on the second substrate 200 side.

[0077] For example, when the twist angle is set to 65° instead of 70°, the alignment directions of the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side and the two-frequency driving liquid crystal molecules 312 on the second substrate 200 side change so that the angle formed by the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side and the two-frequency driving liquid crystal molecules 312 on the second substrate 200 side becomes smaller, but the average liquid crystal alignment direction does not change. The same thing occurs depending on the concentration of the chiral agent added to the liquid crystal material, but the average liquid crystal alignment direction does not change. Therefore, in this embodiment, attention is paid to the average liquid crystal alignment direction 310A, rather than the alignment directions of the two-frequency driving liquid crystal molecules 311 on the first substrate 100 side and the two-frequency driving liquid crystal molecules 312 on the second substrate 200 side.

[0078] The material of the weakly anchoring horizontal alignment film is not particularly limited, and known materials can be used. (See paragraphs 0077 to 0078 of Japanese Patent Application No. 2021-196017). Also, in order to improve reliability and productivity, it is preferably composed of two or more polymers. Also, in order to improve panel strength (seal adhesion), it is desirable to use a material having a polymerizable site that chemically bonds to the sealant.

[0079] The first weakly anchoring horizontal alignment film 411 preferably has an azimuthal anchoring energy of less than 1×10 -4 J / m 2 In such a manner, the polarization modulation performance can be further improved. The second weakly anchoring horizontal alignment film 421 has an azimuthal anchoring energy of 1×10-4 J / m 2 It is preferably less than this. By adopting such an aspect, the polarization modulation performance can be further improved.

[0080] The azimuth anchoring energy can be calculated by various known methods, such as the torque balance method, the Néel wall method, the calculation from the electric field response threshold, the calculation from the rotating magnetic field, etc. The azimuth anchoring energy described in this specification is calculated using the calculation method from the electric field response threshold. The lower limit of the azimuth anchoring energy of the weakly anchoring alignment film is not particularly limited, but the azimuth anchoring energy of the weakly anchoring alignment film is, for example, 1×10 -10 J / m 2 or more.

[0081] The azimuth anchoring energy of the first weakly anchoring horizontal alignment film 411 is 1×10 -10 J / m 2 or more and 1×10 -4 J / m 2 It is preferably less than this, and 1×10 -8 J / m 2 or more and 1×10 -5 J / m 2 It is more preferably less than this. By adopting such an aspect, polarization modulation and non-polarization modulation can be effectively switched over a wide band.

[0082] The azimuth anchoring energy of the second weakly anchoring horizontal alignment film 421 is 1×10 -10 J / m 2 or more and 1×10 -4 J / m 2 It is preferably less than this, and 1×10 -8 J / m 2 or more and 1×10 -5 J / m 2 It is more preferably less than this. By adopting such an aspect, polarization modulation and non-polarization modulation can be effectively switched over a wide band.

[0083] The ratio of the azimuth anchoring energy of the second weakly-anchored horizontal alignment film 421 to the azimuth anchoring energy of the first weakly-anchored horizontal alignment film 411 (i.e., (the azimuth anchoring energy of the second weakly-anchored horizontal alignment film 421) / (the azimuth anchoring energy of the first weakly-anchored horizontal alignment film 411)) is preferably 10 or less. By adopting such an embodiment, the alignment stability can be further improved. The ratio of the azimuth anchoring energy of the second weakly-anchored horizontal alignment film 421 to the azimuth anchoring energy of the first weakly-anchored horizontal alignment film 411 is more preferably 8 or less, and even more preferably 6 or less.

[0084] The ratio of the azimuth anchoring energy of the second weakly-anchored horizontal alignment film 421 to the azimuth anchoring energy of the first weakly-anchored horizontal alignment film 411 is preferably, for example, 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more.

[0085] The ratio of the azimuth anchoring energy of the second weakly-anchored horizontal alignment film 421 to the azimuth anchoring energy of the first weakly-anchored horizontal alignment film 411 is preferably 0.1 or more and 10 or less, more preferably 0.3 or more and 8 or less, and even more preferably 0.5 or more and 6 or less.

[0086] The weakly-anchored alignment film can be formed by performing an alignment treatment, or can be formed without performing an alignment treatment. Specifically, the weakly-anchored alignment film may be a rubbed alignment film, a photo-alignment film, or an untreated alignment film without any alignment treatment.

[0087] The first weakly-anchored horizontal alignment film 411 and the second weakly-anchored horizontal alignment film 421 are preferably untreated alignment films that have not been subjected to an alignment process. That is, the first weakly-anchored horizontal alignment film 411 and the second weakly-anchored horizontal alignment film 421 preferably do not have uniaxial orientation. By adopting such an aspect, the alignment stability can be further improved.

[0088] The first weakly-anchored horizontal alignment film 411 and the second weakly-anchored horizontal alignment film 421 preferably have an in-plane retardation Re of less than 1 nm. By adopting such an aspect, the alignment stability can be further improved.

[0089] The untreated alignment film can be obtained, for example, by forming an alignment film material containing an alignment film polymer on a substrate. Examples of the alignment film polymer include polyimide, polyhexyl methacrylate, and the like. The alignment film polymer contained in the untreated alignment film may be of one type or two or more types.

[0090] In addition to polyimide and polyhexyl methacrylate, the alignment film polymer contained in the untreated alignment film also includes the polymers described in WO 2017 / 034023. Among them, polyalkylene oxides such as polyethylene glycol and polypropylene glycol are preferable.

[0091] The horizontal alignment film has a function of horizontally aligning the two-frequency driving liquid crystal molecules in the liquid crystal layer with respect to the surface of the horizontal alignment film when no voltage is applied. Here, the fact that the two-frequency driving liquid crystal molecules are horizontally aligned with respect to the surface of the horizontal alignment film means that the pretilt angle of the two-frequency driving liquid crystal molecules is 0° or more and 5° or less with respect to the surface of the horizontal alignment film, preferably 0° or more and 2° or less, and more preferably 0° or more and 1° or less. The pretilt angle of the two-frequency driving liquid crystal molecules means the angle at which the major axis of the two-frequency driving liquid crystal molecules inclines with respect to the main plane of the alignment film when no voltage is applied to the liquid crystal layer.

[0092] The first weakly anchoring horizontal alignment film 411 preferably contains a polymer having at least one of the groups represented by the following structural formula (P1) and the group represented by the following structural formula (P2). By adopting such an embodiment, the alignment stability can be further improved.

[0093]

Chemical formula

[0094]

Chemical formula

[0095] The second weakly anchoring horizontal alignment film 421 preferably contains a polymer having at least one of the groups represented by the above structural formula (P1) and the group represented by the above structural formula (P2). By adopting such an embodiment, the polarization modulation performance and the alignment stability can be further improved.

[0096] The first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421 preferably each contain a polymer having at least one of the groups represented by the above structural formula (P1) and the group represented by the above structural formula (P2). By adopting such an embodiment, the polarization modulation performance and the alignment stability can be further improved. The structure of the polymer contained in the first weakly anchoring horizontal alignment film 411 and the structure of the polymer contained in the second weakly anchoring horizontal alignment film 421 may be the same or different from each other. It is more preferable that they are the same because the anchoring energies of the first weakly anchoring film and the second weakly anchoring film can be made the same. Also, from the viewpoint of productivity, it is more preferable that they are the same.

[0097] The light incident on the liquid crystal element 10 is preferably circularly polarized light. By adopting such an aspect, a liquid crystal element 10 capable of switching the polarization state of circularly polarized light can be realized.

[0098] FIG. 5 is a schematic cross-sectional view showing an example of the weak anchoring alignment film provided in the liquid crystal element of Embodiment 1. At least one of the first weak anchoring horizontal alignment film 411 and the second weak anchoring horizontal alignment film 421 (the first weak anchoring horizontal alignment film 411 in this embodiment) is in contact with the comb-shaped electrode 11 and contains at least two types of polymers having different refractive indexes from each other. Among the at least two types of polymers, the polymer having the smallest refractive index is preferably in contact with the liquid crystal layer 300.

[0099] Since the transparent electrode (comb-shaped electrode 11) has a large refractive index with respect to the glass substrate (first support substrate 110 and second support substrate 210) and the liquid crystal layer 300, optical losses due to unnecessary diffraction, haze, unnecessary reflection, etc. are large. However, by adjusting the refractive index of the alignment film material and applying it to the surface of the transparent electrode (comb-shaped electrode 11), the difference in refractive index between the layers can be reduced, and these optical losses can be reduced. That is, at least one of the first weak anchoring horizontal alignment film 411 and the second weak anchoring horizontal alignment film 421 (the first weak anchoring horizontal alignment film 411 in this embodiment) is in contact with the comb-shaped electrode 11 and contains at least two types of polymers having different refractive indexes from each other. Among the at least two types of polymers, the polymer having the smallest refractive index is in contact with the liquid crystal layer 300, whereby the difference in refractive index between the layers can be reduced and the optical loss can be reduced.

[0100] As shown in FIG. 1, the liquid crystal element 10 of the present embodiment includes a retardation film 500 on at least one side opposite to the liquid crystal layer 300 of the first substrate 100 and on the side opposite to the liquid crystal layer 300 of the second substrate 200. The retardation film 500 may be disposed on both sides opposite to the liquid crystal layer 300 of the first substrate 100 and on the side opposite to the liquid crystal layer 300 of the second substrate 200, but is preferably disposed on one side. By adopting such a mode, the productivity of the liquid crystal element 10 can be improved.

[0101] The retardation film 500 is disposed on one side opposite to the liquid crystal layer 300 of the first substrate 100 and on the side opposite to the liquid crystal layer 300 of the second substrate 200. The retardation film 500 has a first quarter-wave film 12 and a second quarter-wave film 13 in order from the side closer to the liquid crystal layer 300. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider band. Hereinafter, a mode in which the liquid crystal element 10 includes a liquid crystal cell 11C, a first quarter-wave film 12, and a second quarter-wave film 13 in order from the incident side to the emission side will be described.

[0102] When no voltage is applied to the comb-shaped electrode 11 or when driving is performed at a frequency lower than the crossover frequency of the two-frequency driving liquid crystal molecules 310 (also referred to as low-frequency driving), the circularly polarized light (for example, right circularly polarized light) incident on the liquid crystal cell 11C becomes first linearly polarized light after passing through the liquid crystal cell 11C. Further, the first linearly polarized light passes through the first quarter-wave film 12 and the second quarter-wave film 13, and is converted into circularly polarized light (for example, left circularly polarized light) having a polarization state different from that of the circularly polarized light incident on the liquid crystal cell 11C in a wide band. In this way, in the first state, polarization modulation in which the circularly polarized light incident on the liquid crystal element 10 is converted into circularly polarized light having a different polarization state (for example, right circularly polarized light is converted into left circularly polarized light) and then emitted is realized in a wide band.

[0103] In addition, for the voltage application state of the comb-shaped electrode 11, circularly polarized light (for example, right circularly polarized light) incident on the liquid crystal cell 11C becomes linearly polarized light having a polarization direction orthogonal to the polarization direction of the first linearly polarized light in a plan view after passing through the liquid crystal cell 11C. That is, the second state can be realized. Further, the second linearly polarized light passes through the first quarter-wave plate 12 and the second quarter-wave plate 13, and is emitted in a wide band while remaining circularly polarized light (for example, right circularly polarized light) having the same polarization state as the circularly polarized light incident on the liquid crystal cell 11C. In this way, in the second state, polarization non-modulation in which the circularly polarized light incident on the liquid crystal element 10 is emitted while remaining in the same polarization state (for example, remaining right circularly polarized light) is realized in a wide band.

[0104] In the present embodiment, a mode including the liquid crystal cell 11C, the first quarter-wave plate 12, and the second quarter-wave plate 13 in this order from the incident side to the emission side will be described. However, the stacking order of these may be reversed. Specifically, the second quarter-wave plate 13, the first quarter-wave plate 12, and the liquid crystal cell 11C may be provided in this order from the incident side to the emission side. Also in this case, in the first state, polarization modulation in which the circularly polarized light incident on the liquid crystal element 10 is converted into circularly polarized light having a different polarization state (for example, right circularly polarized light is converted into left circularly polarized light) and emitted is realized in a wide band, and in the second state, polarization non-modulation in which the circularly polarized light incident on the liquid crystal element 10 is emitted while remaining in the same polarization state (for example, remaining right circularly polarized light) is realized in a wide band. When the stacking order is reversed, the slow axes 12A of the first quarter-wave plate 12 and the slow axis 13A of the second quarter-wave plate 13 are appropriately adjusted.

[0105] FIG. 6 is a diagram showing Stokes plots of the respective layers in the first state of the liquid crystal element according to Embodiment 1. FIG. 6 shows the polarization state (the role of each layer) when passing through each layer in the first state. The principle of polarization modulation of the liquid crystal element 10 according to Embodiment 1 will be described in detail using the Poincaré sphere of FIG. 6.

[0106] As shown in (1) of FIG. 6, right circularly polarized light (S3 = +1) is incident on the liquid crystal cell 11C.

[0107] After passing through the 70°-twisted liquid crystal cell 11C, it is once converted to the polarization state of the plot in (2) of FIG. 6. The points of each plot represent plots with different wavelengths from 380 nm to 780 nm. Near a wavelength of 550 nm, it is linearly polarized (on the equator on the Poincaré sphere), but at other wavelengths, it is plotted in the northern hemisphere of the Poincaré sphere and is elliptically polarized.

[0108] Thereafter, it passes through the first quarter-wave plate 12 (specifically, a quarter-wave plate with inverse wavelength dispersion) and becomes the plot in (3) of FIG. 6.

[0109] Furthermore, when it passes through the second quarter-wave plate 13 (specifically, a quarter-wave plate with flat wavelength dispersion), as shown in the plot in (4) of FIG. 6, almost all wavelengths are emitted as left-circularly polarized light (the south pole position on the Poincaré sphere). That is, it can be seen that modulation from right-circularly polarized light to left-circularly polarized light has been performed.

[0110] Similarly, in the second state (when not modulated), after passing through the 70°-twisted liquid crystal cell 11C, it becomes linearly polarized once. However, since the entire orientation of the liquid crystal cell 11C is rotated by 90°, it becomes linearly polarized light with an angle approximately 90° different from that in the first state (when modulated). Then, after passing through the first quarter-wave plate 12 and the second quarter-wave plate 13, all wavelengths become right-circularly polarized light. That is, right-circularly polarized light can be emitted as right-circularly polarized light, and it becomes non-modulated.

[0111] In this way, in the first state and the second state, the orientation of the two-frequency-driven liquid crystal molecules 310 with a 70° twist is the same, and the entire system is in a relationship where they are different by 90°. When the liquid crystal element 10 of the present embodiment is used, two states of the first state and the second state can be reversibly switched, and a broadband thin variable half-wave plate (sHWP: Switchable Half Wave Plate) element can be realized both when the polarization is not modulated and when the polarization is modulated. Note that which driving state is the modulated state and which is the non-modulated state can be changed by the retardation films (the first quarter-wave plate 12 and the second quarter-wave plate 13) and the arrangement of the substrates.

[0112] The retardation film 500 is, for example, a quarter-wave film. The quarter-wave film (specifically, the first quarter-wave film 12 and the second quarter-wave film 13) may be any film that imparts an in-plane retardation of 20 nm or more and 240 nm or less to light with a wavelength of at least 550 nm.

[0113] Examples of the material of the quarter-wave film include a photopolymerizable liquid crystal material. Examples of the structure of the photopolymerizable liquid crystal material include a structure having a photopolymerizable group such as an acrylate group or a methacrylate group at the end of the skeleton of the liquid crystal molecule.

[0114] The quarter-wave film can be formed, for example, by the following method. First, a photopolymerizable liquid crystal material is dissolved in an organic solvent such as propylene glycol monomethyl ether acetate (PGMEA). Next, the obtained solution is applied onto the surface of a substrate (for example, a polyethylene terephthalate (PET) film) to form a coating film of the solution. Then, a quarter-wave film is formed by performing pre-baking, light irradiation (for example, ultraviolet irradiation), and final baking on the coating film of this solution in this order.

[0115] Alternatively, a chiral agent may be added to the above photopolymerizable liquid crystal material, and a polymerized liquid crystal polymer twisted at 70° may be used as the quarter-wave film.

[0116] As the quarter-wave film, for example, a stretched polymer film can also be used. Examples of the material of the polymer film include cycloolefin polymer, polycarbonate, polysulfone, polyethersulfone, polyethylene terephthalate, polyethylene, polyvinyl alcohol, norbornene, triacetyl cellulose, diacetyl cellulose, and the like.

[0117] The first quarter-wave film 12 preferably has reverse wavelength dispersion characteristics. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider bandwidth. Here, in this specification, the "wavelength dispersibility of the retardation film" refers to the correlation between the absolute value of the retardation imparted by the retardation film and the wavelength of the incident light. In the visible light region, the property that the absolute value of the retardation imparted by the retardation film does not change even when the wavelength of the incident light changes is called "flat wavelength dispersion characteristics". Also, in the visible light region, the property that the absolute value of the retardation imparted by the retardation film decreases as the wavelength of the incident light increases is called "positive wavelength dispersion characteristics", and in the visible light region, the property that the absolute value of the retardation imparted by the retardation film increases as the wavelength of the incident light increases is called "reverse wavelength dispersion characteristics".

[0118] The in-plane retardation of the first quarter-wave film 12 at a wavelength of 450 nm with respect to the in-plane retardation at a wavelength of 550 nm is preferably 0.7 times or more and 1 time or less. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0119] The in-plane retardation of the first quarter-wave film 12 at a wavelength of 650 nm with respect to the in-plane retardation at a wavelength of 550 nm is preferably 1 time or more and 1.3 times or less. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0120] The in-plane retardation of the first quarter-wave film 12 at a wavelength of 550 nm is preferably 30 nm or more and 230 nm or less. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0121] When the azimuth angle of the alignment direction 311A of the two-frequency driven liquid crystal molecules 311 on the first substrate 100 side in the first state is 0°, the azimuth angle of the slow axis (the slow axis 12A of the first quarter-wave plate 12 in this embodiment) of the quarter-wave plate farther from the light emission side among the first quarter-wave plate 12 and the second quarter-wave plate 13 is preferably 48° or more and 66° or less. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider band.

[0122] The second quarter-wave plate 13 preferably has a flat wavelength dispersion characteristic. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider band.

[0123] The in-plane retardation of the second quarter-wave plate 13 at a wavelength of 550 nm is preferably 110 nm or more and 175 nm or less. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider band.

[0124] When the azimuth angle of the alignment direction 311A of the two-frequency driven liquid crystal molecules 311 on the first substrate 100 side in the first state is 0°, the azimuth angle of the slow axis (the slow axis 13A of the second quarter-wave plate 13 in this embodiment) of the quarter-wave plate closer to the light emission side among the first quarter-wave plate 12 and the second quarter-wave plate 13 is preferably 3° or more and 22° or less. By adopting such a mode, polarization modulation and non-polarization modulation can be switched in a wider band.

[0125] The angle formed by the slow axis 12A of the first quarter-wave plate 12 and the slow axis 13A of the second quarter-wave plate 13 is preferably 40° or more and 50° or less, more preferably 42° or more and 48° or less, still more preferably 44° or more and 46° or less, and particularly preferably 45°.

[0126] (Modification 1 of Embodiment 1) FIG. 7 is a schematic cross-sectional view of a liquid crystal element according to Modification 1 of Embodiment 1. The retardation film 500 of Embodiment 1 described above is composed of two quarter-wave films. On the other hand, the retardation film 500 of this modification is composed of a single quarter-wave film. Specifically, as shown in FIG. 7, the retardation film 500 of this modification is disposed on one side opposite to the liquid crystal layer 300 of the first substrate 100 and opposite to the liquid crystal layer 300 of the second substrate 200, and the retardation film 500 is a quarter-wave film 14. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0127] The quarter-wave film 14 preferably has reverse wavelength dispersion characteristics. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0128] The in-plane retardation of the quarter-wave film 14 at a wavelength of 450 nm with respect to the in-plane retardation at a wavelength of 550 nm is preferably 0.7 times or more and 1 time or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0129] The in-plane retardation of the quarter-wave film 14 at a wavelength of 650 nm with respect to the in-plane retardation at a wavelength of 550 nm is preferably 1 time or more and 1.3 times or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0130] The in-plane retardation of the quarter-wave film 14 at a wavelength of 550 nm is preferably 30 nm or more and 230 nm or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0131] When the azimuth angle of the alignment direction 311A of the dual-frequency driving liquid crystal molecules 311 on the side of the first substrate 100 in the first state is set to 0°, the azimuth angle of the slow axis of the quarter-wave film 14 is preferably 2° or more and 22° or less. By adopting such an embodiment, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0132] (Modification Example 2 of Embodiment 1) FIG. 8 is a schematic cross-sectional view of a liquid crystal element according to Modification Example 2 of Embodiment 1. The retardation film 500 of Embodiment 1 described above is composed of two first quarter-wave films 12 and a second quarter-wave film 13. On the other hand, the retardation film 500 of this modification is composed of a positive A plate and a negative A plate. Specifically, as shown in FIG. 8, the retardation film 500 of this embodiment is disposed on one side opposite to the liquid crystal layer 300 of the first substrate 100 and on the side opposite to the liquid crystal layer 300 of the second substrate 200. The retardation film 500 has a positive A plate 15 and a negative A plate 16 in order from the side closer to the liquid crystal layer 300. By adopting such an embodiment, polarization modulation and non-polarization modulation can be switched in a wider bandwidth. Hereinafter, an embodiment in which the liquid crystal element 10 includes a liquid crystal cell 11C, a positive A plate 15, and a negative A plate 16 in order from the incident side to the emission side will be described.

[0133] The positive A plate 15 is a layer that satisfies nx>ny=nz. The in-plane retardation of the positive A plate 15 at a wavelength of 550 nm is preferably 30 nm or more and 230 nm or less. By adopting such an embodiment, polarization modulation and non-polarization modulation can be switched in a wider bandwidth.

[0134] When the azimuth angle of the alignment direction 311A of the dual-frequency driven liquid crystal molecules 311 on the side of the first substrate 100 in the first state is 0°, the azimuth angle of the slow axis of the film on the side farther from the light emission side of the positive A plate 15 and the negative A plate 16 (the positive A plate 15 in this embodiment) is preferably 43° or more and 63° or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched over a wider band.

[0135] The negative A plate 16 is a layer satisfying nz = nx > ny. The in-plane retardation of the negative A plate 16 at a wavelength of 550 nm is preferably 30 nm or more and 230 nm or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched over a wider band.

[0136] When the azimuth angle of the alignment direction 311A of the dual-frequency driven liquid crystal molecules 311 on the side of the first substrate 100 in the first state is 0°, the azimuth angle of the slow axis of the film on the side closer to the light emission side of the positive A plate 15 and the negative A plate 16 (the negative A plate 16 in this embodiment) is preferably more than 0° and 20° or less. By adopting such an aspect, polarization modulation and non-polarization modulation can be switched over a wider band.

[0137] (Modification Example 3 of Embodiment 1) FIG. 9 is a perspective schematic view of a liquid crystal element according to Modification Example 3 of Embodiment 1. FIG. 10 is a cross-sectional schematic view of a liquid crystal element according to Modification Example 3 of Embodiment 1. FIG. 11 is a cross-sectional schematic view of a variable focus element provided with electrodes only on the incident-side substrate.

[0138] In the liquid crystal element 10 of the above Embodiment 1, the first substrate 100 disposed on the incident side has the comb-shaped electrodes 11, and the second substrate 200 disposed on the emission side does not have the comb-shaped electrodes. On the other hand, in the liquid crystal element 10 of this modification example, as shown in FIGS. 9 and 10, the first substrate 100 disposed on the incident side does not have the comb-shaped electrodes 11, and the second substrate 200 disposed on the emission side has the comb-shaped electrodes 11. Also by adopting such an aspect, the alignment stability can be improved.

[0139] As shown in FIG. 10, the first substrate 100 or the second substrate 200 of the liquid crystal element 10 of this modified example includes a curved flexible printed circuit board 10F, and the comb-shaped electrode 11 is provided only on the substrate located in the bending direction of the flexible printed circuit board (FPC: Flexible Printed Circuit) 10F among the first substrate 100 and the second substrate 200. Here, when driving the liquid crystal element 10, as shown in FIGS. 10 and 11, the FPC 10F is pressure-bonded to the liquid crystal element 10, and a voltage is supplied from an external circuit for driving. For example, when applied to a head-mounted display (HMD: Head Mounted Display) or the like, it is necessary to bend the FPC 10F in order to house it in the housing of the headset. Usually, since the temple part of the HMD has a circuit mechanism, it is bent to the emission side. At this time, if there is an electrode on the incident side, as shown in FIG. 11, it is necessary to pressure-bond the FPC 10F to the substrate on the incident side, and peeling of the FPC 10F is likely to occur due to the stress during bending. However, by adopting a configuration in which the electrode substrate is provided on the emission side so as to be bent to the emission side as in this modified example having the configuration of FIG. 10, the reliability of the device can be improved.

[0140] In this specification, the "bending direction of the FPC" means the direction in which the FPC bends when the liquid crystal element is viewed in cross section.

[0141] (Modified Example 4 of Embodiment 1) FIG. 12 is a perspective schematic view of a liquid crystal element according to Modified Example 4 of Embodiment 1. The liquid crystal element 10 of the above Embodiment 1 has the comb-shaped electrode 11 only on one substrate. On the other hand, in this modified example, as shown in FIG. 12, the comb-shaped electrode 11 has a first substrate side comb-shaped electrode 120 provided on the first substrate 100 and a second substrate side comb-shaped electrode 220 provided on the second substrate 200, and the extending direction 120A of the first substrate side comb-shaped electrode 120 is parallel to the extending direction 220A of the second substrate side comb-shaped electrode 220. By adopting such an aspect, the alignment stability can also be improved.

[0142] FIG. 13 is a graph showing the liquid crystal alignment direction with respect to the thickness direction of the liquid crystal layer of the liquid crystal element according to Embodiment 1. FIG. 14 is a graph showing the liquid crystal alignment direction with respect to the thickness direction of the liquid crystal element according to Modification 4 of Embodiment 1. As shown in FIGS. 13 and 14, in this modification having comb electrodes on both substrates, the twist change of the two-frequency driven liquid crystal molecules 310 from the first substrate 100 to the second substrate 200 may have a weakened portion compared to Embodiment 1 having comb electrodes only on one side substrate. When realizing the modulation state with the voltage off, since the twist alignment is achieved only by the chiral agent added to the two-frequency driven liquid crystal molecules, the twist occurs with a uniform change amount from the first substrate 100 to the second substrate 200. On the other hand, when the voltage between the first substrate 100 and the second substrate 200 is turned on, there is a region where the twist change becomes gentle once in the bulk portion. At this time, the modulation characteristics of circularly polarized light can be improved. The alignment direction of the two-frequency driven liquid crystal molecules in the middle of the bulk may only have a relaxed twist, or there may be a region where the twist does not occur for a certain period.

[0143] (Embodiment 2) In this embodiment, the features specific to this embodiment will be mainly described, and the description of the content overlapping with Embodiment 1 and its modifications above will be omitted. This embodiment is substantially the same as Embodiment 1 and its modifications above, except that it further includes a Pancharatnam Berry lens layer.

[0144] FIG. 15 is a schematic cross-sectional view of the variable focus element according to Embodiment 2. As shown in FIG. 15, the variable focus element 30 of this embodiment includes a liquid crystal element 10 and a Pancharatnam Berry (PB) lens layer 20 disposed outside the liquid crystal element 10. As described above, the liquid crystal element 10 can modulate circularly polarized light. Further, since the PB lens layer 20 has different focal lengths for right circularly polarized light and left circularly polarized light, by combining the liquid crystal element 10 and the PB lens layer 20, a variable focus element 30 with variable focus in a wide band can be realized.

[0145] The PB lens 20-layer has the function of condensing and diverging circularly polarized light. The PB lens layer 20 can be manufactured, for example, by the method described in International Publication No. 2019 / 189818.

[0146] (Modification Example 1 of Embodiment 2) FIG. 16 is a schematic cross-sectional view of a variable focal element according to Modification Example 1 of Embodiment 2. The PB lens layer 20 of the above Embodiment 2 is disposed outside the liquid crystal element 10 (that is, out-cell). On the other hand, as shown in FIG. 16, the variable focal element 30 of this modification includes a liquid crystal element 10 and a PB lens layer 21 disposed inside the liquid crystal element 10. Even in such a mode, a variable focal element 30 that is variable in focus over a wide band can be realized.

[0147] The in-cell PB lens layer 21 is, in other words, an in-cell retardation layer patterned so that the slow axis direction rotates in the plane. The PB lens layer 21 can be formed in-cell, for example, by applying a photosensitive material for forming an in-cell PB lens containing a polymer on the second substrate 200, forming a film for forming a PB lens, and then performing an alignment treatment on the film for forming a PB lens.

[0148] (Embodiment 3) In this embodiment, the features specific to this embodiment will be mainly described, and the descriptions of the contents overlapping with those of the above Embodiment 1 and its modification examples, and the above Embodiment 2 and its modification examples will be omitted. In this embodiment, a head-mounted display including the above liquid crystal element 10 will be described.

[0149] FIG. 17 is a schematic diagram for explaining an example of a head-mounted display according to Embodiment 3. As shown in FIG. 17, the head-mounted display 1 of this embodiment includes a liquid crystal element 10. The head-mounted display 1 is a display device that can be worn on the head of the user U, and is a binocular type and an immersive display that completely covers the user's eyes when worn on the head.

[0150] The head-mounted display 1 has a function of displaying an image for the user U, and includes a video output unit 10Z including a liquid crystal element 10, an audio output unit 20Z having a function of generating sounds such as voices, music, and sound effects, a mounting unit 30Z that integrally connects the video output unit 10Z and the audio output unit 20Z and detachably mounts them on the head of the user U, and a face cushion 40Z disposed between the video output unit 10Z and the face of the user U. The video output unit 10Z of the present embodiment is composed of one display.

[0151] Further, the head-mounted display 1 includes a drive unit 50Z that outputs a video display signal and an audio output signal, and the drive unit 50Z is connected to the video output unit 10Z and the audio output unit 20Z by wire or wirelessly. Examples of the wireless communication method include Bluetooth (registered trademark).

[0152] Hereinafter, the effects of the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0153] (Comparative Example 1) FIG. 18 is a schematic cross-sectional view of a liquid crystal element according to Comparative Example 1. FIG. 19 is a perspective schematic view of the liquid crystal element according to Comparative Example 1. FIG. 20 is a schematic view for explaining the alignment of liquid crystal molecules in the first state and the second state of the liquid crystal element according to Comparative Example 1. FIG. 21 is a view showing the axial orientation of the liquid crystal element according to Comparative Example 1.

[0154] A comparative example 1 liquid crystal element 10R corresponding to Example 1 of the above Patent Document 3 shown in FIGS. 18 to 21 was fabricated. The liquid crystal element 10R of Comparative Example 1 has, in order from the incident side to the emission side, a liquid crystal cell 11R having a first substrate 100R, a liquid crystal layer 300R containing liquid crystal molecules 310R, and a second substrate 200R, a quarter-wave film with inverse wavelength dispersion as a first quarter-wave film 12R, and a quarter-wave film with flat wavelength dispersion as a second quarter-wave film 13R. The azimuth angle of the slow axis of the quarter-wave film with inverse wavelength dispersion (the slow axis 12AR of the first quarter-wave film 12R) was 57.2°, and the azimuth angle of the slow axis of the quarter-wave film with flat wavelength dispersion (the slow axis 13AR of the second quarter-wave film 13R) was 12.2. The liquid crystal element 10R of Comparative Example 1 was specifically fabricated as follows.

[0155] A first substrate 100R including a first support substrate 110R and a first comb electrode 120R and a second substrate 200R including a second support substrate 210R and a second comb electrode 220R were prepared. The electrode direction of the first substrate 100R (the extending direction 120AR of the first comb electrode 120R) and the electrode direction of the second substrate 200R (the extending direction 220AR of the second comb electrode 220R) were formed so as to have the angular relationship shown in FIG. 21 when bonded together. Further, a photospacer with a height of 3.6 μm was disposed on the second substrate 200R.

[0156] Next, PMMA (polymethyl methacrylate) was deposited on both the first substrate 100R including the first comb electrode 120R and the second substrate 200R including the second comb electrode 220R. Subsequently, a sealing material was drawn on the second substrate 200R, and the first substrate 100R and the second substrate 200R were bonded together with a liquid crystal material (liquid crystal layer 300R) sandwiched therebetween to fabricate a liquid crystal cell 11R.

[0157] Here, as the liquid crystal material, a mixture in which 5 wt% of dodecyl acrylate (C12A) and a chiral agent S-811 were mixed with a positive-type liquid crystal molecule having a positive dielectric anisotropy (Δn = 0.066) was used. The concentration of the chiral agent was set so that the twist angle between the upper and lower substrates in the liquid crystal cell was 70°.

[0158] After heating the liquid crystal cell 11R to the isotropic phase state, while applying a voltage to the first substrate 100R, it was cooled to room temperature, and a uniformly horizontally aligned liquid crystal cell 11R was obtained, which includes a first weakly anchoring horizontal alignment film 411R and a second weakly anchoring horizontal alignment film 421R. Further, a quarter-wave film with inverse wavelength dispersion (first quarter-wave film 12R) and a quarter-wave film with flat wavelength dispersion (second quarter-wave film 13R) were attached to the liquid crystal cell 11R obtained above, and a liquid crystal element (sHWP element) 10R of Comparative Example 1 was obtained.

[0159] FIG. 22 is a graph for explaining the voltage applied to the liquid crystal element according to Comparative Example 1. As shown in FIG. 22, when a voltage is applied to the second substrate 200R with respect to the liquid crystal element 10R of Comparative Example 1, as shown in FIG. 20, due to the horizontal electric field on the second substrate 200R side, the liquid crystal molecules 312R on the second substrate 200R side are aligned in the 70° direction. Then, when the voltage of the second substrate 200R is weakened (not zero), the liquid crystal molecules 312R on the second substrate 200R side remain aligned in the 70° direction along the electric field direction, and the liquid crystal molecules 311R on the first substrate 100 side slide due to the chiral twisting force added to the liquid crystal material and are aligned in the 0° direction. This was the first state. Incidentally, after this, even when the voltage was turned off, the alignment state of this first state was maintained.

[0160] In the reverse manner to the above, when a voltage is applied to the first substrate 100R and then weakened, as shown in FIG. 20, the liquid crystal molecules 311R on the first substrate 100R side face the 90° direction (azimuth angle 90°), and the liquid crystal molecules 312R on the second substrate 200R side face the 160° direction (azimuth angle 160°) due to the chiral force. This was the second state. Thus, the liquid crystal element 10R of Comparative Example 1 was able to switch between the second state and the first state by applying a voltage to the first substrate 100R or by applying a voltage to the second substrate 200R.

[0161] As shown in FIG. 21, the first state and the second state were the same in that the liquid crystal molecules 311R on the first substrate 100R side and the liquid crystal molecules 312R on the second substrate 200R side were twisted by 70°, but the whole system was in a relationship of 90° rotation.

[0162] As described above, the liquid crystal element 10R of Comparative Example 1 included positive-type liquid crystal molecules 310R and had electrodes on each of the first substrate 100R and the second substrate 200R. The stretching direction of the electrodes and the alignment direction of the liquid crystal molecules located at the interface with the electrodes were parallel or perpendicular. The average liquid crystal alignment direction of all the liquid crystal molecules contained in the liquid crystal layer was not parallel or perpendicular to the stretching direction of the first comb-shaped electrode 120R and was not parallel or perpendicular to the stretching direction of the second comb-shaped electrode 220R. In the liquid crystal element 10R of Comparative Example 1, a driving method as shown in FIG. 22 was adopted, and the alignment of the liquid crystal molecules was maintained even when the voltage was cut off.

[0163] FIG. 23 is a photograph showing the evaluation result of the alignment stability of the liquid crystal element of Comparative Example 1. After leaving the liquid crystal element 10R of Comparative Example 1 at room temperature for one month, the liquid crystal element 10R was observed with a polarizing microscope. As a result, alignment defects were confirmed in the liquid crystal element 10R of Comparative Example 1 as shown in FIG. 23.

[0164] (Example 1) FIG. 24 is a schematic diagram for explaining the alignment of liquid crystal molecules when the liquid crystal cell included in the liquid crystal element according to Example 1 was heated to the isotropic phase state and then rapidly cooled. FIG. 25 is a schematic diagram for explaining the alignment of liquid crystal molecules in the first state and the second state of the liquid crystal element according to Example 1. FIG. 26 is a diagram showing the axial orientation of the liquid crystal element according to Example 1. The liquid crystal element 10 of Example 1 corresponding to Embodiment 1 shown in FIGS. 1 to 4 and FIGS. 24 to 26 was manufactured as follows.

[0165] First, a first substrate 100 having a comb electrode 11 in which a comb-shaped pixel electrode and a common electrode are provided such that their combs are engaged with each other, and a second substrate 200 having a photo spacer and no electrode were prepared. The electrode width of the comb electrode 120 was 3 μm, and the slit width (also referred to as a space) was 9 μm. The azimuth angle in the extending direction 11A of the comb electrode 11 was set to 125° - 305°.

[0166] Next, a weakly anchoring horizontal alignment film with an extremely small alignment control force was formed on both the first substrate 100 and the second substrate 200. That is, a first weakly anchoring horizontal alignment film 411 was formed on the first substrate 100, and a second weakly anchoring horizontal alignment film 421 was formed on the second substrate 200. No photo-alignment treatment or rubbing treatment was performed on the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421, and the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421 did not have uniaxial orientation. That is, the in-plane anisotropy of the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421 was small. The in-plane retardation of the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421 was both 0.8 nm. The azimuthal anchoring energy of the first weakly anchoring horizontal alignment film 411 was 5×10 -6 J / m 2 and the azimuthal anchoring energy of the second weakly anchoring horizontal alignment film 421 was 5×10 -6 J / m 2 In this example, a weakly anchoring film (returning to the initial alignment when the voltage is OFF) of the type applied to the substrate was used as in a normal alignment film. The first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421 were each composed of one type of polymer.

[0167] Subsequently, a sealing material was drawn on the second substrate 200, and the first substrate 100 and the second substrate 200 were bonded together with a liquid crystal material (liquid crystal layer 300 including dual-frequency driving liquid crystal molecules 310) sandwiched therebetween to fabricate a liquid crystal cell 11C. Here, as the liquid crystal material, a material in which a chiral agent was added to the dual-frequency driving liquid crystal molecules was used. The concentration of the chiral agent was adjusted so that the twist angle between the upper and lower substrates in the liquid crystal cell was 70°.

[0168] In the liquid crystal element 10 of this embodiment, since the alignment films on both sides (the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421) are weakly anchoring alignment films, alignment defects occur in the normal liquid crystal production process. Therefore, in this embodiment, after heating this liquid crystal cell 11C to the isotropic phase state, while applying a voltage to the comb-shaped electrode 11 provided on the first substrate 100, the temperature was lowered to obtain a liquid crystal element 10 without alignment defects. The voltage applied at this time was less than the crossover frequency of the dual-frequency driving liquid crystal (specifically, 30 Hz, 5 V, and the sign of Δε of the liquid crystal molecules was positive). As a result of performing this process, as shown in FIG. 24, a uniform alignment was obtained in a state where the average liquid crystal alignment direction of the dual-frequency driving liquid crystal molecules 310 when the voltage was off was perpendicular to the extending direction 11A of the comb-shaped electrode 11. The average liquid crystal alignment direction was measured by Axoscan as described above.

[0169] A quarter-wave film with inverse wavelength dispersion (first quarter-wave film 12) and a quarter-wave film with flat wavelength dispersion (second quarter-wave film 13) were attached to the liquid crystal cell 11C obtained above to obtain the liquid crystal element (sHWP element) 10 of Example 1. Both the first quarter-wave film 12 and the second quarter-wave film 13 in this embodiment were positive A plates. The azimuth angle of the slow axis of the quarter-wave film with inverse wavelength dispersion (slow axis 12A of the first quarter-wave film 12) was 57.2°, and the azimuth angle of the slow axis of the quarter-wave film with flat wavelength dispersion (slow axis 13A of the second quarter-wave film 13) was 12.2°.

[0170] In the liquid crystal element 10 of this embodiment, when no voltage is applied (also referred to as voltage-off) or when driving at a frequency lower than the crossover frequency of the two-frequency driving liquid crystal (also referred to as low-frequency driving), the relationship between the components is as shown in the first state of FIG. 25. At this time, the incident circularly polarized light is emitted as the opposite circularly polarized light (modulation state). On the other hand, when driving at a frequency equal to or higher than the crossover frequency of the two-frequency driving liquid crystal (for example, 300 kHz) (also referred to as high-frequency driving), the relationship between the components is as shown in the second state of FIG. 25. At this time, the incident circularly polarized light is emitted while maintaining the direction of the circularly polarized light (non-modulation state). Further, when changing from the high-frequency driving state to the voltage-off state or the low-frequency driving state, the modulation state is restored. In this way, a device capable of switching circularly polarized light by changing the driving frequency of the liquid crystal molecules or the application / non-application of voltage has been obtained.

[0171] In this embodiment, large and small voltages such as those in Comparative Example 1 are unnecessary, and the first and second states can be switched by switching the on and off of the voltage applied to the electrode provided only on one substrate.

[0172] FIG. 27 is a photograph showing the evaluation result of the alignment stability of the liquid crystal element of Example 1. Similar to Comparative Example 1, after leaving the liquid crystal element 10 of Example 1 at room temperature for one month, the liquid crystal element 10 was observed with a polarizing microscope. As a result, it was confirmed that in the liquid crystal element 10 of Example 1, as shown in FIG. 27, a uniform alignment without alignment defects was maintained.

[0173] Regarding the phase modulation element of Example 1, the optical state was evaluated using Axoscan manufactured by Axometrics, and the circular polarization state of the light emitted when right circularly polarized light (light with S3 = +1) was incident was evaluated. The evaluation conditions were three visible wavelengths of 450 nm / 550 nm / 650 nm and an incident azimuth angle of 0° to 40°. As a result, the worst value of the Stokes parameter S3 among all these conditions was -0.92 in the modulation state and 0.94 in the non-modulation state, and it was confirmed that both states had excellent modulation characteristics. In this evaluation, light with S3 = +1 was incident on the liquid crystal element, and it can be said that when the emitted light is close to S3 = -1, it is an excellent modulation state, and when it is close to S3 = +1, it is an excellent non-modulation state. A case where the absolute value is 0.9 or more was regarded as passing.

[0174] (Example 2) A liquid crystal element of Example 2 was fabricated in the same manner as in Example 1, except that the electrode width of the comb-shaped electrode 11 was set to 3 μm and the slit width was set to 13 μm. That is, in Example 2, the space of the comb-shaped electrode 120 was made wider compared to Example 1.

[0175] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 2. As a result, the liquid crystal element of Example 2 had S3 = -0.95 in the modulation state and S3 = 0.96 in the non-modulation state, and had excellent polarization modulation characteristics. Similar to Example 1, in Example 2 as well, it is considered that the liquid crystal molecules (bulk) away from the substrate interface react to the applied voltage. In this case, making the space wider allows the liquid crystal molecules to rotate uniformly in the plane, and the value of S3 can be made even better. Therefore, it is considered that Example 2 achieved better polarization modulation characteristics than Example 1.

[0176] (Example 3) A liquid crystal element of Example 3 was fabricated in the same manner as in Example 1, except that the electrode width of the comb-shaped electrode 11 was set to 2 μm and the slit width was set to 5 μm. That is, in Example 3, the comb-shaped electrode 11 had a narrower pitch compared to Example 1.

[0177] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 3. As a result, the liquid crystal element of Example 3 had S3 = -0.91 in the modulated state and S3 = 0.92 in the non-modulated state, and had excellent polarization modulation characteristics. It was found that when the pitch was narrow, the voltage could be reduced, but the circular polarization modulation characteristics deteriorated slightly compared to Example 1.

[0178] (Example 4) FIG. 28 is a diagram showing the axial orientation of the liquid crystal element according to Example 4. The liquid crystal element 10 of Example 4 corresponding to Modification 1 of Embodiment 1 shown in FIGS. 7 and 28 was fabricated. The liquid crystal element 10 of Example 4 had the same configuration as Example 1 except that it did not include the first quarter-wave plate 12 and the second quarter-wave plate 13, and included a quarter-wave plate 14. The quarter-wave plate 14 was a quarter-wave plate with reverse wavelength dispersion, and the azimuth angle of the slow axis 14A was 12.2°.

[0179] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 4. As a result, the liquid crystal element of Example 4 had S3 = -0.9 in the modulated state and S3 = 0.9 in the non-modulated state, and had excellent polarization modulation characteristics.

[0180] (Example 5) FIG. 29 is a diagram showing the axial orientation of the liquid crystal element according to Example 5. The liquid crystal element 10 of Example 5 corresponding to Modification 2 of Embodiment 1 shown in FIGS. 8 and 29 was fabricated. The liquid crystal element 10 of Example 5 had the same configuration as Example 1 except that it did not include the first quarter-wave plate 12 and the second quarter-wave plate 13, and included a positive A plate 15 and a negative A plate 16.

[0181] The in-plane retardation (Re) of the positive A plate 15 at a wavelength of 550 nm was 140 nm, the in-plane retardation at a wavelength of 450 nm with respect to the in-plane retardation at a wavelength of 550 nm (Re(450) / Re(550)) was 1.01, the in-plane retardation at a wavelength of 650 nm with respect to the in-plane retardation at a wavelength of 550 nm (Re(650) / Re(550)) was 0.99, and the azimuth angle of the slow axis 15A was 53°.

[0182] For the negative A plate 16, the in-plane retardation (Re) at a wavelength of 550 nm was 120 nm, the in-plane retardation at a wavelength of 450 nm with respect to the in-plane retardation at a wavelength of 550 nm (Re(450) / Re(550)) was 1.08, the in-plane retardation at a wavelength of 650 nm with respect to the in-plane retardation at a wavelength of 550 nm (Re(650) / Re(550)) was 0.96, and the azimuth angle of the slow axis 16A was 10°.

[0183] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 5. As a result, the liquid crystal element of Example 5 had S3 = -0.94 in the modulated state and S3 = 0.95 in the unmodulated state, and had excellent polarization modulation characteristics.

[0184] From Examples 4 and 5, it was found that the effect of the present invention can be exhibited even with only one 1 / 4 wavelength film, but the polarization modulation characteristics are further improved when a plurality of 1 / 4 wavelength films are laminated. Also, it was found that a configuration including both the positive A plate 15 (axis azimuth of the slow axis 15A = 53°) and the negative A plate 16 (axis azimuth of the slow axis 16A = 10°) is preferable for widening the viewing angle.

[0185] (Example 6) A liquid crystal element 10 of Example 6 having the same configuration as Example 1 was fabricated, except that it included the liquid crystal cell 11C of Modification 3 of Embodiment 1 shown in FIG. 9. The liquid crystal element 10 of this example had the same configuration as Example 1, except that the first substrate 100 did not include the comb-shaped electrode 11 and the second substrate 200 included the comb-shaped electrode 11.

[0186] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 6. As a result, the liquid crystal element 10 of Example 6 had S3 = -0.92 in the modulated state and S3 = 0.94 in the unmodulated state, and had excellent polarization modulation characteristics.

[0187] As shown in FIG. 15, a PB lens layer 20 was attached to the liquid crystal element (phase modulation element) 10 of this embodiment, and a liquid crystal lens (variable focus element 30) having the PB lens layer 20 on the outside of the liquid crystal element 10 was fabricated. The variable focus element 30 of this embodiment included a comb electrode 11 only on the substrate (second substrate 200) located in the bending direction of the FPC 10F, and had the PB lens layer 20 on the outside of the liquid crystal element 10. It was confirmed that the liquid crystal lens (variable focus element 30) of this embodiment had variable focus in a wide band.

[0188] FIG. 30 is a schematic cross-sectional view of a variable focus element according to Example 6. FIG. 31 is a schematic cross-sectional view of a variable focus element having electrodes only on the incident-side substrate. The liquid crystal elements 10 of Examples 1 to 5 included a comb electrode 11 (IPS electrode) on the substrate (first substrate 100) located on the side opposite to the bending direction of the FPC 10F (i.e., the incident side), but the liquid crystal element 10 of this embodiment included a comb electrode 11 (IPS electrode) on the substrate (second substrate 200) located in the bending direction of the FPC 10F (i.e., the emission side), and it was found that this configuration was also suitable.

[0189] (Example 7) A variable focus element 30 of Example 7 corresponding to Modification 1 of Embodiment 2 shown in FIG. 16 was fabricated. The variable focus element 30 of Example 7 had the same configuration as the variable focus element 30 of Example 6 except that the first quarter-wave film 12 and the second quarter-wave film 13 were arranged on the side opposite to the liquid crystal layer 300 of the first substrate 100, and the PB lens layer 21 was arranged between the liquid crystal layer 300 and the second substrate 200.

[0190] In Example 7, a retardation film (a first quarter-wave film 12 and a second quarter-wave film 13) was provided on the incident side, a PB lens layer 21 was provided between the second substrate 200 located on the emission side and the liquid crystal layer 300, and the second substrate 200 was provided with electrodes. When the PB lens layer 21 is disposed inside (in-cell) the liquid crystal element 10, since it is necessary to complete the phase modulation before the light passes through the PB lens layer 21, the retardation film (the first quarter-wave film 12 and the second quarter-wave film 13) was provided on the incident side. The variable focus element 30 (liquid crystal lens) of this example was confirmed to have variable focus in a wide band.

[0191] FIG. 32 is a schematic cross-sectional view for explaining the wiring of the variable focus element according to Example 7. Similar to Example 6, for the variable focus element of this example as well, considering the strength against the bending of the FPC as shown in FIG. 32, the laminated structure of this example in which electrodes are disposed on the second substrate 200 located on the emission side (the bending direction of the FPC10F) is considered to be suitable.

[0192] (Example 8) A liquid crystal element 10 of Example 8 having the same configuration as that of Example 1 was fabricated, except that the liquid crystal cell 11C of Modification 4 of Embodiment 1 shown in FIG. 12 was provided. The liquid crystal element 10 of this example had the same configuration as that of Example 1, except that the first substrate 100 was provided with the comb-shaped electrodes 120 on the first substrate side and the second substrate 200 was provided with the comb-shaped electrodes 220 on the second substrate side. The extending directions (the directions of the slits) of the comb-shaped electrodes 120 on the first substrate side and the comb-shaped electrodes 220 on the second substrate side were set parallel.

[0193] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 8. As a result, the liquid crystal element of Example 6 had S3 = -0.92 in the modulated state and S3 = 0.95 in the non-modulated state, and had excellent polarization modulation characteristics.

[0194] (Example 9) FIG. 33 is a diagram showing the axial orientation of the liquid crystal element according to Example 9. The liquid crystal element 10 of Example 9 shown in FIG. 33 was fabricated. The liquid crystal element 10 of Example 9 had the same configuration as the liquid crystal element 10 of Example 5, except that the azimuth angle of the slow axis 15A of the positive A plate 15 was 53°, the azimuth angle of the slow axis 16A of the negative A plate 16 was 10°, and the azimuth angle of the stretching direction 120A of the comb-shaped electrode 120 was 125°.

[0195] In Examples 1 to 8, it was possible to realize a modulated state when the voltage was off or at low-frequency driving, and a non-modulated state at high-frequency driving. However, in this example, it was possible to realize a non-modulated state when the voltage was off or at low-frequency driving, and a modulated state at high-frequency driving.

[0196] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 9. As a result, the liquid crystal element of Example 9 had excellent polarization modulation characteristics with S3 = -0.92 in the modulated state and S3 = 0.94 in the non-modulated state.

[0197] (Example 10) The liquid crystal element 10 of Example 10 was fabricated in the same manner as in Example 1, except that the first weakly anchoring horizontal alignment film 411 and the second weakly anchoring horizontal alignment film 421 were each formed using a material in which two types of polymers with different refractive indices were mixed.

[0198] As shown in FIG. 5, in the liquid crystal element of Example 10, the polymer with a high refractive index was segregated on the side of the substrate (the first substrate 100), and the polymer with a low refractive index was segregated on the side in contact with the liquid crystal layer 300.

[0199] Similar to Example 1, the Stokes parameter S3 was also evaluated for Example 10. As a result, the liquid crystal element of Example 10 had excellent polarization modulation characteristics with S3 = -0.92 in the modulated state and S3 = 0.94 in the non-modulated state.

[0200] Also, the haze of the liquid crystal elements of Example 1 and Example 10 was evaluated. As a result, the haze of the liquid crystal element of Example 1 was 4.3%, and the haze of the liquid crystal element of Example 10 was 2.1%. The haze of the liquid crystal element of Example 10 was improved compared to Example 1.

[0201] Haze refers to the value determined from Haze (%) = 100×(diffuse transmittance) / (total light transmittance) by measuring the diffuse transmittance and the total light transmittance. The measurement of the diffuse transmittance and the total light transmittance was performed using a haze meter (product name: NDH-2000) manufactured by Nippon Denshoku Industries Co., Ltd.

Explanation of Reference Numerals

[0202] 1: Head-mounted display 10, 10R: Liquid crystal element 10F: Flexible printed circuit board (FPC) 10Z: Video output section 11, 120, 120R, 220, 220R: Comb electrodes 11A, 120A, 120AR, 220A, 220AR: Extension direction 11C, 11R: Liquid crystal cell 11E: Linear electrode section 11S: Slit section 12, 12R, 13, 13R, 14: Quarter-wave film 12A, 12AR, 13A, 13AR, 14A, 15A, 16A: Slow axis 15: Positive A plate 16: Negative A plate 20, 21: Pancharatnam Berry (PB) lens layer 20Z: Acoustic output section 30Z: Mounting section 40Z: Face cushion 50Z: Driving unit 30: Variable focus element 100, 100R: First substrate 110, 110R, 210, 210R: Support substrate 200, 200R: Second substrate 300, 300R: Liquid crystal layer 310, 311, 312: Two-cycle driven liquid crystal molecules 310A: Average liquid crystal alignment direction 310R, 311R, 312R: Liquid crystal molecules 311A, 311B, 312A, 312B: Alignment directions 411, 411R, 421, 421R: Weak anchoring horizontal alignment film 500: Phase difference film E: Electric field U: User

Claims

1. A first substrate, a first weakly-anchored horizontal alignment film with an azimuthal anchoring energy of less than 1×10−4 J / m2, a liquid crystal layer containing dual-frequency driven liquid crystal molecules, a second weakly-anchored horizontal alignment film with an azimuthal anchoring energy of less than 1×10−4 J / m2, and a second substrate, provided in this order, wherein at least one of the first substrate and the second substrate has a comb-shaped electrode for generating an electric field in the liquid crystal layer, the comb-shaped electrode is provided on only one of the first substrate and the second substrate, or has a first-substrate-side comb-shaped electrode provided on the first substrate and a second-substrate-side comb-shaped electrode provided on the second substrate, and the extending direction of the first-substrate-side comb-shaped electrode is parallel to the extending direction of the second-substrate-side comb-shaped electrode, the dual-frequency driven liquid crystal molecules are twisted and oriented between the first substrate and the second substrate in both the voltage-applied state and the voltage-non-applied state, and the twist direction in the voltage-applied state is the same as the twist direction in the voltage-non-applied state, a liquid crystal element in which, in the voltage-non-applied state, the alignment direction of the dual-frequency driven liquid crystal molecules located at the center in the thickness direction of the liquid crystal layer is orthogonal or parallel to the extending direction of the comb-shaped electrode.

2. The liquid crystal element according to claim 1, wherein the first weakly-anchored horizontal alignment film contains a polymer having at least one of a group represented by the following structural formula (P1) and a group represented by the following structural formula (P2). 【Chemical Formula 1】 【Chemical Formula 2】 (In the above structural formula, X has at least one group selected from an ether group, an ester group, and an amide group, and R １ , R ２ , R ３ and R ４ each independently represents a hydrocarbon group, and Y is a carbon atom or a silicon atom.)

3. The liquid crystal element according to claim 1, wherein the second weakly-anchored horizontal alignment film contains a polymer having at least one of a group represented by the following structural formula (P1) and a group represented by the following structural formula (P2). [Chemical Formula 3] 【Chemical Formula 4】 (In the above structural formula, X has at least one group among an ether group, an ester group, and an amide group, and R １ , R ２ , R ３ and R ４ each independently represents a hydrocarbon group, and Y is a carbon atom or a silicon atom.)

4. The liquid crystal element according to claim 1, wherein the first weakly-anchored horizontal alignment film and the second weakly-anchored horizontal alignment film do not have uniaxial orientation.

5. The liquid crystal element according to claim 1, wherein the first weakly-anchored horizontal alignment film and the second weakly-anchored horizontal alignment film have an in-plane retardation of less than 1 nm.

6. The liquid crystal element according to claim 1, wherein, in the voltage-non-applied state, the alignment direction of the dual-frequency driven liquid crystal molecules located at the center in the thickness direction of the liquid crystal layer is orthogonal to the extending direction of the comb-shaped electrode.

7. The liquid crystal element according to claim 1, wherein the comb-shaped electrode is provided on only one of the first substrate and the second substrate.

8. The comb-shaped electrodes include a comb-shaped electrode on the first substrate side provided on the first substrate and a comb-shaped electrode on the second substrate side provided on the second substrate. The liquid crystal element according to claim 1, wherein the extending direction of the comb-shaped electrode on the first substrate side is parallel to the extending direction of the comb-shaped electrode on the second substrate side.

9. The liquid crystal element according to claim 1, wherein the ratio of the electrode width to the slit width of the comb-shaped electrode (electrode width: slit width) is 1:2 to 1:

6.

10. The liquid crystal element according to claim 1, wherein the ratio of the thickness of the liquid crystal layer to the slit width of the comb-shaped electrode (thickness of liquid crystal layer: slit width) is 1:2.5 to 1:

10.

11. Furthermore, the liquid crystal element according to claim 1 includes a retardation film on at least one of the side of the first substrate opposite to the liquid crystal layer and the side of the second substrate opposite to the liquid crystal layer.

12. The liquid crystal element according to claim 11, wherein the retardation film has a first quarter-wave film and a second quarter-wave film in order from the side closer to the liquid crystal layer.

13. At least one of the first weakly anchoring horizontal alignment film and the second weakly anchoring horizontal alignment film is in contact with the comb-shaped electrode and contains at least two types of polymers having different refractive indices. The liquid crystal element according to claim 1, wherein the polymer having the smallest refractive index among the at least two types of polymers is in contact with the liquid crystal layer.

14. The liquid crystal element according to claim 1, wherein the ratio of the azimuth anchoring energy of the second weakly anchoring horizontal alignment film to the azimuth anchoring energy of the first weakly anchoring horizontal alignment film is 10 or less.

15. Furthermore, the first substrate or the second substrate includes a curved flexible printed circuit board. The liquid crystal element according to claim 1, wherein the comb-shaped electrode is provided only on the substrate located in the bending direction of the flexible printed circuit board among the first substrate and the second substrate.

16. A head-mounted display including the liquid crystal element according to any one of claims 1 to 15.

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