Liquid crystal light control device

Abstract

This liquid crystal light control device has at least one liquid crystal panel. The at least one liquid crystal panel includes: a first substrate provided with a first electrode including a belt-shaped pattern, and a first alignment film covering the first electrode; a second substrate provided with a second electrode including a belt-shaped pattern, and a second alignment film covering the second electrode; and a liquid crystal layer between the first substrate and the second substrate. The liquid crystal layer has a thickness of 10 μm or more, liquid crystal molecules are twist-aligned from the first substrate side to the second substrate side, and the pretilt angle of the liquid crystal molecules defined by the first alignment film and the second alignment film is two degrees or more but less than eight degrees.

Description

LCD light control device

[0001] An embodiment of the present invention relates to a liquid crystal light control device that controls the distribution of light emitted from a light source by utilizing the electro-optic effect of liquid crystals.

[0002] A liquid crystal light control device has been disclosed in which a plurality of liquid crystal panels are stacked and the light distribution state of the liquid crystal in each liquid crystal panel is controlled to control the light distribution state of lighting (see, for example, Patent Document 1).

[0003] International Publication No. 2022 / 176684

[0004] The liquid crystal panel that constitutes the liquid crystal light control device is irradiated with strong light emitted from a light source, which makes it easy for liquid crystal alignment disorder to occur inside the liquid crystal panel. Since liquid crystal alignment disorder affects the light distribution characteristics of the liquid crystal light control device, how to prevent this is an issue. In view of this problem, an object of one embodiment of the present invention is to provide a more reliable liquid crystal light control device.

[0005] A liquid crystal light control device according to one embodiment of the present invention has at least one liquid crystal panel, the at least one liquid crystal panel including a first substrate provided with a first electrode including a strip-shaped pattern and a first alignment film covering the first electrode, a second substrate provided with a second electrode including a strip-shaped pattern and a second alignment film covering the second electrode, and a liquid crystal layer between the first and second substrates, the liquid crystal layer having a thickness of 10 μm or more, liquid crystal molecules being twist-aligned from the first substrate side to the second substrate side, and a pretilt angle of the liquid crystal molecules defined by the first alignment film and the second alignment film being 2 degrees or more and less than 8 degrees.

[0006] FIG. 1 shows an overview of a liquid crystal light control device according to one embodiment of the present invention. FIG. 2 shows a perspective view of a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention. FIG. 3 shows an electrode structure of a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention. FIG. 4 shows an electrode structure of a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention. FIG. 5 is a diagram explaining the operation of a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention. FIG. 6 is a diagram explaining the operation of a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention. FIG. 7 is a diagram explaining the relationship between the chiral material contained in a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention and the thickness of a liquid crystal layer. FIG. 8 is a diagram explaining the voltage applied to a liquid crystal panel constituting a liquid crystal light control element according to one embodiment of the present invention and the resulting state of light distribution control. FIG. 9 is a diagram explaining an example of light distribution control by a liquid crystal light control element according to one embodiment of the present invention.

[0007] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. For clarity of explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual form, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the previous drawings are designated by the same reference numerals (or reference numerals with a, b, etc. suffixed thereto), and detailed descriptions may be omitted as appropriate. Furthermore, the letters "first" and "second" attached to each element are convenient labels used to distinguish each element and have no further meaning unless otherwise specified.

[0008] In this specification, when a component or region is referred to as being "on (or under)" another component or region, unless otherwise specified, this includes not only the case where it is directly above (or directly under) the other component or region, but also the case where it is above (or under) the other component or region, i.e., the case where another component is included between the component or region and above (or under) the other component or region.

[0009] In this specification, "light distribution" refers to the degree of spread of light emitted from a light source, i.e., the distribution of luminous intensity (light intensity) in each direction, in the usual sense, and controlling the light distribution means intentionally controlling the degree of spread of light emitted from a light source.

[0010] In this specification, "optical rotation" refers to the phenomenon in which the polarization axis of a linearly polarized component is rotated when passing through a liquid crystal layer.

[0011] In this specification, the "alignment direction" of an alignment film refers to the direction in which liquid crystal molecules are aligned when the alignment film is subjected to a treatment (e.g., a rubbing treatment) that imparts an alignment restraining force to the alignment film and aligns the liquid crystal molecules on the alignment film. When the treatment performed on the alignment film is a rubbing treatment, the alignment direction of the alignment film is usually the rubbing direction.

[0012] In this specification, the "extension direction" of a strip electrode refers to the direction in which the long side of a pattern having a short side (width) and a long side (length) extends when the strip electrode is viewed in a plan view.

[0013] 1. Overview of a Liquid Crystal Light Control Device Fig. 1 is a perspective view showing the configuration of a liquid crystal light control device 100 according to one embodiment of the present invention. Liquid crystal light control device 100 includes a liquid crystal light control element 102 and a control circuit 104. Liquid crystal light control element 102 is made up of multiple liquid crystal panels. Fig. 1 shows an example in which liquid crystal light control element 102 is made up of a first liquid crystal panel 1021, a second liquid crystal panel 1022, a third liquid crystal panel 1023, and a fourth liquid crystal panel 1024.

[0014] The first liquid crystal panel 1021, the second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024 are flat panels. The liquid crystal light control element 102 has a structure in which the flat surfaces of the first liquid crystal panel 1021, the second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024 are arranged so as to overlap each other. The first liquid crystal panel 1021 and the second liquid crystal panel 1022, the second liquid crystal panel 1022 and the third liquid crystal panel 1023, and the third liquid crystal panel 1023 and the fourth liquid crystal panel 1024 are bonded together with a transparent adhesive (not shown). From the side of the light source 106, the first liquid crystal panel 1021, the second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024 are stacked in this order.

[0015] The liquid crystal light control element 102 is driven by a control circuit 104. In other words, control signals for driving each liquid crystal panel are output from the control circuit 104. As shown in Fig. 1, the control circuit 104 is connected to the first liquid crystal panel 1021 by a first flexible wiring board F1, to the second liquid crystal panel 1022 by a second flexible wiring board F2, to the third liquid crystal panel 1023 by a third flexible wiring board F3, and to the fourth liquid crystal panel 1024 by a fourth flexible wiring board F4.

[0016] The liquid crystal light control device 100 has a function of controlling the degree of spread of light emitted from the light source 106, i.e., the luminous intensity distribution of light spreading in a predetermined direction. The light source 106 is disposed on the rear side of the liquid crystal light control element 102. The light emitted from the light source 106 is emitted to the outside (illumination space) through the liquid crystal light control element 102. That is, the light emitted from the light source 106 passes through the first liquid crystal panel 1021, the second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024 in this order before being emitted to the outside. When the light emitted from the light source 106 is irradiated onto the liquid crystal light control element 102, the light passes through the first liquid crystal panel 1021, the second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024 in this order before being emitted to the outside.

[0017] There is no limitation on the configuration of the light source 106. The light source 106 is composed of components such as a light-emitting element, such as a light-emitting diode, a halogen lamp, a tungsten lamp, a mercury lamp, or a fluorescent lamp, and a reflector. The light source 106 may be a white light source, or a light source that emits dimmed light such as daylight white or warm white. An optical element such as a lens may be provided between the light source 106 and the liquid crystal light control element 102.

[0018] As will be described in detail below, the liquid crystal light control device 100 has a function of controlling the spread of light emitted from the light source 106 by the liquid crystal light control element 102. The liquid crystal light control element 102 has a function of forming a light distribution pattern such as a square, cross, or line shape on the irradiation surface with the light emitted from the light source 106, based on a control voltage output from the control circuit 104.

[0019] 2. Liquid Crystal Panel Figure 2 shows a perspective view of the first liquid crystal panel 1021 that constitutes the liquid crystal light control element 102. For the sake of explanation, Figure 2 shows the X, Y, and Z axis directions. The X and Y axes are orthogonal in a plan view, and the Z axis extends in a direction normal to the X-Y plane. In the following explanation, the X axis direction, Y axis direction, and Z axis direction are used to specify directions, but these expressions can also be replaced with expressions such as the X axis direction being the first direction, the Y axis direction being the second direction, and the Z axis direction being the third direction or the up-down direction.

[0020] The first liquid crystal panel 1021 includes a first substrate S11, a second substrate S12, a first electrode E11, a second electrode E12, a first alignment film AL11, a second alignment film AL12, and a first liquid crystal layer LC1. The first substrate S11 is provided with a first electrode E11 and a first alignment film AL11, and the second substrate S12 is provided with a second electrode E12 and a second alignment film AL12. The first alignment film AL11 is provided to cover the first electrode E11, and the second alignment film AL12 is provided to cover the second electrode E12. The first substrate S11 and the second substrate S12 are spaced apart from each other and arranged opposite each other. The first electrode E11 and the second electrode E12 are arranged on the inner surface of the first substrate S11 and the second substrate S12 facing each other. A first liquid crystal layer LC1 is provided between the first substrate S11 and the second substrate S12.

[0021] The first electrode E11 includes a first strip electrode E11A and a second strip electrode E11B each having a plurality of strip patterns. The second electrode E12 includes a third strip electrode E12A and a fourth strip electrode E12B each having a plurality of strip patterns. The first strip electrodes E11A and the second strip electrodes E11B are alternately arranged on the insulating surface of the first substrate S11, and the third strip electrodes E12A and the fourth strip electrodes E12B are alternately arranged on the insulating surface of the second substrate S12.

[0022] The longitudinal direction of the multiple strip patterns of the first strip electrode E11A and the second strip electrode E11B extends in the X-axis direction. The longitudinal direction of the multiple strip patterns of the third strip electrode E12A and the fourth strip electrode E12B extends in the Y-axis direction. Therefore, the direction in which the multiple strip patterns of the third strip electrode E12A and the fourth strip electrode E12B extend is orthogonal (intersects at 90 degrees) to the direction in which the multiple strip patterns of the first strip electrode E11A and the second strip electrode E11B extend. Note that the relative arrangement of the first strip electrode E11A and the second strip electrode E11B and the third strip electrode E12A and the fourth strip electrode E12B is not limited to being orthogonal, and may be changed within a range of ±10 degrees from 90 degrees.

[0023] Furthermore, the strip-shaped patterns of each of these strip-shaped electrodes may extend in a predetermined direction while being partially bent. In this case, the strip-shaped patterns have multiple extension directions in their longitudinal direction, and each extension direction may be inclined by approximately ±10 degrees with respect to the X-axis direction or the Y-axis direction. Similarly, the strip-shaped electrodes may have a configuration in which the strip-shaped patterns extend in a predetermined direction while being partially curved. In this case, the direction of the tangent at each position of the strip-shaped pattern is regarded as the extension direction, and each extension direction may be inclined by approximately ±10 degrees with respect to the X-axis direction or the Y-axis direction.

[0024] The direction in which the multiple strip patterns constituting the first strip electrode E11A and the second strip electrode E11B extend may be inclined in the range of 30±10 degrees to 60±10 degrees with respect to the X-axis direction. Similarly, the direction in which the multiple strip patterns constituting the third strip electrode E12A and the fourth strip electrode E12B extend may be inclined in the range of 30±10 degrees to 60±10 degrees with respect to the Y-axis direction.

[0025] The alignment direction ALD1 of the first alignment film AL11 is oriented in a direction (Y-axis direction) intersecting the extension direction of the first strip electrodes E11A and the second strip electrodes E11B, and the alignment direction ALD2 of the second alignment film AL12 is oriented in a direction (X-axis direction) intersecting the extension direction of the third strip electrodes E12A and the fourth strip electrodes E12B. The angle at which the extension direction of the first strip electrodes E11A and the second strip electrodes E11B intersects with the alignment direction ALD1, and the angle at which the extension direction of the third strip electrodes E12A and the fourth strip electrodes E12B intersects with the alignment direction ALD2 can be set within a range of 90±10 degrees.

[0026] The first substrate S11 and the second substrate S12 are disposed opposite each other with a gap of 10 μm or more. For example, the first substrate S11 and the second substrate S12 are disposed with a gap of 10 μm or more and 1000 μm or less, preferably 20 μm or more and 100 μm or less. A first liquid crystal layer LC1 provided between the first substrate S11 and the second substrate S12 has a thickness D. A first electrode E11, a second electrode E12, a first alignment film AL11, and a second alignment film AL12 are provided between the first substrate S11 and the second substrate S12, but the film thicknesses of these components are negligibly small compared to the gap between the first substrate S11 and the second substrate S12. Therefore, the gap between the first substrate S11 and the second substrate S12 can be considered to be the thickness D of the first liquid crystal layer LC1. That is, the thickness D of the first liquid crystal layer LC1 can be regarded as being 10 μm or more and 1000 μm or less, preferably 20 μm or more and 100 μm or less. Although not shown in FIG. 2, a spacer may be provided between the first substrate S11 and the second substrate S12.

[0027] The liquid crystal material forming the first liquid crystal layer LC1 is, for example, twisted nematic liquid crystal (TN liquid crystal). As shown schematically in FIG. 2, liquid crystal molecules have elongated rod-like structures due to their molecular structure. The rod-like liquid crystal molecules have different physical properties in the long axis direction (parallel to the molecular long axis) and the short axis direction (perpendicular to the molecular long axis). Specifically, it is known that the difference in electrical properties is dielectric anisotropy, and the difference in optical properties is refractive index anisotropy. The liquid crystal panel constituting the liquid crystal light control element 102 is provided with a first alignment film AL11 and a second alignment film AL12 to control the alignment direction of the liquid crystal molecules and the average tilt angle (pretilt angle) relative to the substrate surface.

[0028] As shown in Fig. 2, the liquid crystal molecules LCM have a pretilt angle θp. The pretilt angle θp of the liquid crystal molecules LCM is controlled by the first alignment film AL11 and the second alignment film AL12. The pretilt angle θp refers to the angle θp at which the long axis direction of the liquid crystal molecules rises with respect to the substrate surface, as shown in the inset of Fig. 2. The pretilt angle θp is the angle that the liquid crystal molecules have when no electric field is acting on them (initial alignment state).

[0029] The first alignment film AL11 and the second alignment film AL12 are formed from organic materials. Examples of organic materials include polyimide-based materials. A rubbing process is performed on polyimide-based alignment films to impart alignment control force. The rubbing process involves rubbing the surface of the alignment film while rotating a cloth-wrapped roller at high speed. In the rubbing process, the direction of rubbing with the rubbing roller is the rubbing direction, which is also the alignment direction in which the liquid crystal molecules are oriented. The pretilt angle of the liquid crystal molecules is roughly determined by the material of the alignment film and the liquid crystal material, and fine adjustment of the angle is possible by changing the processing conditions of the rubbing process.

[0030] FIG. 2 shows that the alignment direction ALD1 (rubbing direction) of the first alignment film AL11 is parallel to the Y-axis, and the alignment direction ALD2 (rubbing direction) of the second alignment film AL12 is parallel to the X-axis. Furthermore, as shown in detail in the inset of FIG. 2, the liquid crystal molecules LCM on the first substrate S11 side are aligned in the Y-axis direction and tilted in the Z-axis direction at a pretilt angle θp. Note that the inset of FIG. 2 only shows the state of the liquid crystal molecules LCM on the first alignment film AL11 side, but the same is true on the second alignment film AL12 side. That is, on the first substrate S11 side, the liquid crystal molecules LCM are aligned so that their major axes intersect the longitudinal direction of the strip-shaped pattern of the first electrode E11, and on the second substrate side, the liquid crystal molecules LCM are aligned so that their major axes intersect the longitudinal direction of the strip-shaped pattern of the second electrode, and have a pretilt angle θp.

[0031] The alignment directions ALD1 and ALD2 of the first alignment film AL11 and the second alignment film AL12 may be controlled by a photo-alignment process instead of a rubbing process. The photo-alignment process is a process in which linearly polarized ultraviolet light is irradiated obliquely onto a photosensitive polymer alignment film. In the photo-alignment process, photoreactive molecules are oriented obliquely by the polarization of the linearly polarized light. When liquid crystal molecules come into contact with the alignment film thus formed, the photo-alignment state is transferred to the liquid crystal molecules, making it possible to control their alignment. The photo-alignment process makes it possible to adjust not only the irradiation direction but also the irradiation angle of the linearly polarized light, thereby enabling control of the pretilt angle of the liquid crystal molecules.

[0032] Furthermore, inorganic insulating films may be used as the first alignment film AL11 and the second alignment film AL12. The inorganic insulating film used as the alignment film may have, for example, a groove structure or a column structure. An inorganic insulating film having such a unique structure can be produced by vacuum deposition, more specifically, oblique deposition. There is no limitation on the material for forming the inorganic insulating film; for example, a silicon oxide film can be used.

[0033] Alignment films made of inorganic materials with groove or column structures allow for control of the alignment direction and pretilt angle of liquid crystal molecules. In other words, in oblique deposition, the shape of the groove or column structures can be changed by adjusting the angle between the incident direction of the evaporated particles and the normal direction of the substrate, thereby enabling control of the alignment direction and pretilt angle of liquid crystal molecules.

[0034] 2 again, when no voltage is applied to the first electrode E11 and the second electrode E12, the liquid crystal molecules LCM of the first liquid crystal layer LC1 have a pretilt angle θp in the vicinity of the first alignment film AL11 and the second alignment film AL12 due to the alignment restraining forces of these alignment films, and the long axis directions of the liquid crystal molecules LCM are aligned in the alignment directions ALD1 and ALD2 of the alignment films. Since the alignment direction ALD1 of the first alignment film AL11 and the alignment direction ALD2 of the second alignment film AL12 intersect (are perpendicular to each other), the long axis directions of the liquid crystal molecules LCM gradually change so as to be twisted by 90 degrees from the first substrate S11 to the second substrate S12.

[0035] FIG. 3A shows a plan view of the first substrate S11, and FIG. 3B shows a plan view of the second substrate S12. As shown in FIG. 3A, the first electrode E11 has a structure in which a plurality of first strip electrodes E11A and a plurality of second strip electrodes E11B are alternately arranged. The longitudinal directions of the plurality of first strip electrodes E11A and the plurality of second strip electrodes E11B extend in the X-axis direction. In contrast, the alignment direction ALD1 of the first alignment film AL11 (not shown) extends in the Y-axis direction. That is, the longitudinal direction of the plurality of first strip electrodes E11A and the plurality of second strip electrodes E11B intersects (is perpendicular to) the alignment direction ALD1. Furthermore, as shown in FIG. 3B, the second electrode E12 has a structure in which a plurality of third strip electrodes E12A and a plurality of fourth strip electrodes E12B are alternately arranged. The longitudinal direction of the plurality of third strip electrodes E12A and the plurality of fourth strip electrodes E12B extends in the Y-axis direction. In contrast, the alignment direction ALD2 of the second alignment film AL12 (not shown) extends in the X-axis direction. That is, the longitudinal direction of the plurality of third strip electrodes E12A and the plurality of fourth strip electrodes E12B intersects (is perpendicular to) the alignment direction ALD2.

[0036] As shown in FIG. 3A , the plurality of first strip-shaped electrodes E11A are each connected to a first power supply line PE11, and the plurality of second strip-shaped electrodes E11B are each connected to a second power supply line PE12. The first power supply line PE11 is connected to a first connection terminal T11, and the second power supply line PE12 is connected to a second connection terminal T12. The first connection terminal T11 and the second connection terminal T12 are provided at an end of the first substrate S11. The first substrate S11 is provided with a third connection terminal T13 adjacent to the first connection terminal T11 and a fourth connection terminal T14 adjacent to the second connection terminal T12. The third connection terminal T13 is connected to a fifth power supply line PE15. The fifth power supply line PE15 is connected to a first power supply terminal PT11 provided on the first substrate S11. The fourth connection terminal T14 is connected to a sixth power supply line PE16. The sixth power supply line PE16 is connected to a second power supply terminal PT12 provided on the first substrate S11.

[0037] The same voltage is applied to the multiple first strip electrodes E11A via the first power supply line PE11. The same voltage is applied to the multiple second strip electrodes E11B via the second power supply line PE12. When different voltages are applied to the first connection terminal T11 and the second connection terminal T12, a potential difference occurs between the multiple first strip electrodes E11A and the multiple second strip electrodes E11B, generating an electric field. As a result, an electric field is generated in the horizontal direction (Y-axis direction) by the multiple first strip electrodes E11A and the multiple second strip electrodes E11B.

[0038] As shown in FIG. 3B , the plurality of third strip-shaped electrodes E12A are each connected to a third power supply line PE13, and the plurality of fourth strip-shaped electrodes E12B are each connected to a fourth power supply line PE14. The third power supply line PE13 is connected to the third connection terminal T13, and the fourth power supply line PE14 is connected to the fourth connection terminal T14. The third power supply terminal PT13 is provided at a position corresponding to the first power supply terminal PT11 on the first substrate S11, and the fourth power supply terminal PT14 is provided at a position corresponding to the second power supply terminal PT12 on the first substrate S11. The third power supply terminal PT13 and the first power supply terminal PT11, and the fourth power supply terminal PT14 and the second power supply terminal PT12 are electrically connected. A conductive paste is used for the electrical connection between these power supply terminals. For example, a silver paste is used as the conductive paste.

[0039] When different voltages are applied to the third connection terminal T13 and the fourth connection terminal T14, a potential difference occurs between the third strip electrodes E12A and the fourth strip electrodes E12B, generating an electric field in the horizontal direction (X-axis direction) due to the third strip electrodes E12A and the fourth strip electrodes E12B.

[0040] The first substrate S11 and the second substrate S12 are light-transmitting substrates, such as a glass substrate or a resin substrate. The first electrode E11 and the second electrode E12 are transparent electrodes formed of indium tin oxide (ITO) or indium zinc oxide (IZO). The power supply lines (first power supply line PE11, second power supply line PE12, third power supply line PE13, and fourth power supply line PE14) and connection terminals (first connection terminal T11, second connection terminal T12, third connection terminal T13, and fourth connection terminal T14) are formed of metal materials such as aluminum, titanium, molybdenum, and tungsten. Note that the power supply lines (first power supply line PE11, second power supply line PE12, third power supply line PE13, and fourth power supply line PE14) may be formed of the same transparent conductive film as the first electrode E11 and the second electrode E12. Of course, it is also possible to employ a configuration in which either or both of the first electrode E11 and the second electrode E12 are formed from a metal material or a transparent conductive film having a metal material laminated thereon.

[0041] As shown in FIG. 3A , the first strip electrode E11A and the second strip electrode E11B are arranged with a center-to-center distance W. The center-to-center distance W has a relationship of W = WE + WD, where WE is the width of the first strip electrode E11A and the second strip electrode E11B shown in FIG. 3A and WD is the distance from the end of the first strip electrode E11A to the end of the second strip electrode E11B. The same applies to the center-to-center distance W, width WE, and distance WD of the third strip electrode E12A and the fourth strip electrode E12B shown in FIG. 3B . The width WE of the strip electrodes can be, for example, 4 μm or more, and the electrode distance WD can be the same as or different from the width WE. In the liquid crystal panel constituting the liquid crystal light control element 102, the center-to-center distance W of the strip electrodes and the thickness D of the first liquid crystal layer LC1 (i.e., equivalent to the distance D between the first substrate S11 and the second substrate S12) have a close relationship, and by making the value of D / W equal to or greater than 1, it is possible to sufficiently diffuse (spread in a predetermined direction) light of a predetermined polarization component. For example, when the width WE of the strip electrodes is 4 μm and the electrode distance WD is 4 μm, it is preferable that the thickness D of the first liquid crystal layer LC1 be 12 μm or greater.

[0042] 4A and 4B are diagrams for explaining the operation of the first liquid crystal panel 1021, and show the structure of the first liquid crystal panel 1021 shown in Fig. 2 when viewed from the XA side. Fig. 4A shows a state in which no voltage is applied to the first electrode E11 (first strip electrode E11A and second strip electrode E11B), and Fig. 4B shows a state in which a voltage is applied to the first electrode E11 and a transverse electric field is generated between the first strip electrode E11A and the second strip electrode E11B.

[0043] The first strip-shaped electrode E11A and the second strip-shaped electrode E11B are arranged with a distance WD between them, with the longitudinal direction of the strip-shaped pattern extending in the X-axis direction. Comparing the thickness D of the first liquid crystal layer LC1 with the electrode distance WD between the first electrodes E11, the thickness D of the first liquid crystal layer LC1 is equal to or greater than the electrode distance WD (D≧WD). For example, the thickness D of the first liquid crystal layer LC1 is at least twice the electrode distance WD between the first electrodes E11. For example, when the thickness D of the first liquid crystal layer LC1 is 10 μm, the electrode distance WD can be 5 μm, and when the thickness D of the first liquid crystal layer LC1 is 50 μm, the electrode distance WD can be 10 μm.

[0044] The alignment direction of the first alignment film AL11 extends in the Y-axis direction, and the alignment direction of the second alignment film AL12 extends in the X-axis direction. When no electric field is applied to the first liquid crystal layer LC1 ( FIG. 4A ), the long axes of the liquid crystal molecules LCM have a pretilt angle θp and are aligned in a state twisted 90 degrees from the first substrate S11 side to the second substrate S12 side. In this state, the first liquid crystal layer LC1 has a uniform refractive index distribution. When light is incident on the first liquid crystal panel 1021, the polarized components of the incident light are rotated by the twist of the liquid crystal molecules LCM. In this state, the incident light is rotated but passes through the first liquid crystal layer LC1 without being refracted (or scattered).

[0045] On the other hand, when a voltage is applied to the first electrode E11 and a transverse electric field is generated between the first strip electrode E11A and the second strip electrode E11B, the long axes of the liquid crystal molecules LCM are oriented along the electric field (if the liquid crystal has positive dielectric anisotropy). As a result, as shown in FIG. 4B , regions are formed in which the liquid crystal molecules LCM rise above the first strip electrode E11A and the second strip electrode E11B, and regions are formed between the first strip electrode E11A and the second strip electrode E11B in which the liquid crystal molecules LCM are oriented obliquely along the distribution of the electric field. At this time, if the thickness D of the first liquid crystal layer LC1 is sufficiently large (10 μm or more), i.e., if the thickness D of the first liquid crystal layer LC1 is sufficiently large, the electric field generated by the first electrode E11 does not affect the second substrate S12 side, and the alignment state of the liquid crystal molecules LCM changes only on the first substrate S11 side. In other words, the liquid crystal molecules LCM on the second substrate S12 side are not affected by the electric field and maintain an unchanged alignment.

[0046] As shown in FIG. 4B , when a transverse electric field is generated between the first strip electrode E11A and the second strip electrode E11B, the liquid crystal molecules LCM are oriented such that their long axes are aligned in a convex arc shape along the direction of the electric field. In liquid crystals with dielectric anisotropy, the dielectric constant distribution also changes in an arc shape as the alignment of the liquid crystal molecules LCM changes. When light is incident from the first substrate S11 in this state, the polarized component parallel to the Y-axis direction is diffused radially due to the dielectric constant distribution. Meanwhile, the polarized component parallel to the X-axis direction is not affected by the dielectric constant distribution and enters the first liquid crystal layer LC1 without being diffused. In this way, by aligning the liquid crystal molecules LCM in a specific direction and changing their alignment using a transverse electric field, it is possible to diffuse a specific polarized component of the incident light (widening the luminous intensity distribution).

[0047] 4A and 4B illustrate the effect of the first electrode E11 on the liquid crystal molecules LCM and incident light, but the same applies to the effect that the second electrode E12 of the second substrate S12 has on the first liquid crystal layer LC1. That is, on the second substrate S12 side, the second electrode E12 generates a transverse electric field, which can diffuse the polarized light component parallel to the X-axis direction (widen the luminous intensity distribution).

[0048] As described with reference to FIGS. 4A and 4B , the first liquid crystal panel 1021 can diffuse incident light in a predetermined direction. Therefore, the use of the first liquid crystal panel 1021 makes it possible to control the light distribution state of light emitted from a light source. However, when strong light is irradiated onto the alignment films (first alignment film AL11, second alignment film AL12), the alignment films may be deteriorated due to the influence of that light. This influence can be particularly significant for alignment films formed from organic materials such as polyimide. Even in liquid crystal displays, the alignment films are exposed to backlight light. However, the luminous intensity is lower than that of a light source for illumination, and the light is polarized by a polarizer, so degradation of the alignment film is not a problem. On the other hand, when used for illumination purposes such as the liquid crystal light control element 102 of this embodiment and strong light is incident from a light source, the alignment film is prone to degradation.

[0049] When the alignment film deteriorates, the alignment control force for the liquid crystal molecules LCM decreases, which causes a problem. When the alignment control force decreases, the direction in which the liquid crystal molecules LCM twist becomes unstable, and when the applied voltage is turned off and the electric field is removed, a phenomenon occurs in which the twist direction is reversed (hereinafter also referred to as "reverse twist"), causing the alignment of the liquid crystal molecules LCM to become unstable.

[0050] To cope with this phenomenon, the occurrence of reverse twist can be suppressed by providing the liquid crystal molecules LCM with a pretilt angle θp as shown in this embodiment. If the pretilt angle θp is 2 degrees or more, the occurrence of reverse twist can be reduced, and if it is 3 degrees or more, it can be almost eliminated.

[0051] 4B shows the region where liquid crystal molecules LCM are aligned by the transverse electric field formed by the first strip electrode E11A and the second strip electrode E11B as region A, and the adjacent regions as regions B and C. As described with reference to FIG. 3A, the first substrate S11 has a plurality of first strip electrodes E11A and a plurality of second strip electrodes E11B arranged alternately, so a transverse electric field is also generated in regions B and C adjacent to region A. However, the direction of the transverse electric field (the direction of the electric field lines) is opposite in regions B and C compared to region A. Therefore, as shown in FIG. 4B, alignment defects DF occur on the first strip electrode E11A and the second strip electrode E11B.

[0052] This alignment defect DF occurs at the center of the electrode when the alignment of the liquid crystal molecules LCM has no pretilt angle. However, when the liquid crystal molecules LCM are aligned with a pretilt, instability can become a problem depending on the direction and magnitude of the pretilt. Specifically, it has been found that instability increases when the pretilt angle of the liquid crystal molecules LCM is 8 degrees or more, but no instability problems occur when the pretilt angle is 6 degrees or less.

[0053] From the above, it can be said that the pretilt angle θp of the liquid crystal molecules LCM should be 2 degrees or more and less than 8 degrees, and preferably 3 degrees or more and 6 degrees or less, in order to improve the reliability of the first liquid crystal panel 1021. Note that although Figures 2, 4A, and 4B show the case where the alignment direction of the alignment film is parallel rubbing, it may also be anti-parallel rubbing.

[0054] As described with reference to FIG. 2 , the first liquid crystal layer LC1 in this embodiment is a twisted nematic liquid crystal, which is aligned by a 90-degree twist from the first substrate S11 side to the second substrate S12 side. The first liquid crystal layer LC1 may contain a chiral material to suppress reverse twisting that occurs when the electric field is removed. As shown in FIG. 5 , the thickness D of the first liquid crystal layer LC1 is preferably less than half (½) of the pitch p of the chiral material (D<p / 2), where p is the distance by which the liquid crystal twists 360 degrees due to the chiral material). More preferably, the thickness D of the first liquid crystal layer LC1 is greater than one-eighth (½) of the pitch p of the chiral material and less than one-half (½) of the pitch p (p / 8<D<p / 2). If the thickness D of the first liquid crystal layer LC1 is greater than 1 / 2 of the pitch p of the chiral material, the twist of the liquid crystal may become 270 degrees instead of 90 degrees. Also, in order to realize the effect of adding the chiral material, it is preferable that the thickness D of the first liquid crystal layer LC1 is greater than 1 / 8 of the pitch p.

[0055] 6 shows the first liquid crystal panel 1021, in which the first strip electrodes E11A and second strip electrodes E11B of the first electrode E11 extend in the X-axis direction, and the third strip electrodes E12A and fourth strip electrodes E12B of the second electrode E12 extend in the Y-axis direction. The alignment direction ALD1 of the first alignment film AL1 is parallel to the Y-axis direction, and the alignment direction ALD2 of the second alignment film AL2 is parallel to the X-axis direction. Therefore, the long axes of the liquid crystal molecules LCM on the first substrate S11 side are oriented in the Y-axis direction, and the long axes of the liquid crystal molecules LCM on the second substrate S12 side are oriented in the X-axis direction.

[0056] FIG. 6 also shows a state in which the control circuit 104 applies a high-level voltage VH to the first strip electrode E11A, a low-level voltage VL (VH>VL) to the second strip electrode E11B, a high-level voltage VH to the third strip electrode E12A, and a low-level voltage VL (VH>VL) to the fourth strip electrode E12B.

[0057] Light emitted from the light source has a first polarization component PL1 and a second polarization component PL2, and is incident on the first liquid crystal panel 1021 from the first substrate S11 side. Here, the first polarization component PL1 corresponds to a P wave (having an amplitude in the X-axis direction), and the second polarization component PL2 corresponds to an S wave (having an amplitude in the Y-axis direction). As shown in the table inserted in Fig. 6 , the light incident on the first liquid crystal panel 1021 is subjected to optical effects such as transmission, optical rotation, and diffusion by the first liquid crystal layer LC1.

[0058] Here, "Transmission" in the table refers to the transmission of a given polarization component without changing its polarization axis or light distribution. Furthermore, "Diffusion (Y)" indicates that the polarization component is diffused in a direction parallel to the Y-axis. Although not shown in Figure 6, "Diffusion (X)" indicates that the polarization component is diffused in a direction parallel to the X-axis.

[0059] Because the first polarized component PL1 is a P-wave, its polarization direction intersects with the long axis direction of the liquid crystal molecules LCM on the first electrode E11 side, and it is transmitted as is without being affected by the arc-shaped refractive index distribution formed by the orientation of the liquid crystal molecules LCM. As the first polarized component PL1 travels through the first liquid crystal layer LC1 from the first substrate S11 side to the second substrate S12 side, it is rotated by 90 degrees and transitions to an S-wave state. The polarization direction of the first polarized component PL1 that has transitioned to an S-wave state intersects with the long axis direction of the liquid crystal molecules LCM on the second electrode E12 side, and it is transmitted as is without being affected by the arc-shaped refractive index distribution formed by the orientation of the liquid crystal molecules LCM.

[0060] On the other hand, the second polarized component PL2 is an S-wave, and because its polarization direction on the first electrode E11 side is parallel to the long axis direction of the liquid crystal molecules LCM, it is diffused in the Y-axis direction due to the influence of the arc-shaped refractive index distribution formed by the orientation of the liquid crystal molecules LCM. As the second polarized component PL2 travels through the first liquid crystal layer LC1 from the first substrate S11 side to the second substrate S12 side, it is rotated by 90 degrees and transitions to a P-wave state. Because the polarization direction of the second polarized component PL2 on the second electrode E12 side becomes parallel to the long axis direction of the liquid crystal molecules LCM, it is diffused in the X-axis direction due to the influence of the arc-shaped refractive index distribution formed by the orientation of the liquid crystal molecules LCM.

[0061] In this way, when light enters the first liquid crystal panel 1021 from the first substrate S11 side, the first polarization component PL1 (P wave) is not diffused, but is rotated by the first liquid crystal layer LC1 and emitted in the form of an S wave, and the second polarization component PL2 (S wave) is diffused once in each of the Y-axis direction and the X-axis direction, and is rotated by the first liquid crystal layer LC1 and emitted in the form of a P wave.

[0062] Figure 6 shows an example in which the second polarization component PL2 (S wave) is diffused in the Y-axis and X-axis directions by the first liquid crystal panel 1021, but it is also possible to diffuse the first polarization component PL1 (P wave) by combining multiple liquid crystal panels.

[0063] 4. Operation of Liquid Crystal Light Control Element Figure 7 shows an example of the operation of liquid crystal light control element 102. As explained with reference to Figure 1, liquid crystal light control element 102 is composed of four liquid crystal panels (first liquid crystal panel 1021, second liquid crystal panel 1022, third liquid crystal panel 1023, and fourth liquid crystal panel 1024) having a configuration similar to that of first liquid crystal panel 1021. For the sake of explanation, Figure 7 shows the liquid crystal panels spaced apart, but in actual liquid crystal light control element 102, the liquid crystal panels are bonded together with a light-transmitting adhesive.

[0064] The second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024 have the same configuration as the first liquid crystal panel 1021 shown in Fig. 6. That is, the second liquid crystal panel 20 has a first substrate S21, a second substrate S22, a first electrode E21, a second electrode E22, and a second liquid crystal layer LC2. The third liquid crystal panel 30 has a first substrate S31, a second substrate S32, a first electrode E31, a second electrode E32, and a third liquid crystal layer LC3. The fourth liquid crystal panel 40 has a first substrate S41, a second substrate S42, a first electrode E41, a second electrode E42, and a fourth liquid crystal layer LC4. Note that for simplicity, the alignment films of each liquid crystal panel are omitted from the illustration in Fig. 7.

[0065] The first electrodes E11, E21, E31, E41 are composed of first strip electrodes E11A, E21A, E31A, E41A and second strip electrodes E11B, E21B, E31B, E41B, and these strip electrodes extend in the X-axis direction, and the second electrodes E12, E22, E32, E42 are composed of third strip electrodes E12A, E22A, E32A, E42A and fourth strip electrodes E12B, E22B, E32B, E42B, and these strip electrodes extend in the Y-axis direction.

[0066] A low-level voltage VL, a high-level voltage VH, and a constant voltage CV are applied to each liquid crystal panel as control signals. The low-level voltage VL is, for example, 0 V or -15 V, and the high-level voltage VH is, for example, 30 V (for VL = 0 V) ​​or 15 V (for VL = -15 V). The constant voltage CV is, for example, a voltage signal that is an intermediate voltage between VL1 and VH1 or 0 V (ground).

[0067] 7 shows a state in which a high-level voltage VH and a low-level voltage VL are applied as control signals to the first electrode E11 and the second electrode E12 of the first liquid crystal panel 1021, the first electrode E21 and the second electrode E22 of the second liquid crystal panel 1022, the first electrode E31 and the second electrode E32 of the third liquid crystal panel 1023, and the first electrode E41 and the second electrode E42 of the fourth liquid crystal panel 1024. That is, the liquid crystal molecules are aligned by a transverse electric field on the first substrates S11, S21, S31, S41 side and the second substrates S12, S22, S32, S42 side of each liquid crystal panel.

[0068] 7 shows that light emitted from the light source enters the first liquid crystal panel 1021 and exits the fourth liquid crystal panel 1024. The light emitted from the light source includes a first polarized component PL1 (P wave) and a second polarized component PL2 (S wave), and the table inserted in FIG. 6 shows how the diffusion, optical rotation, and transmission change at each liquid crystal panel.

[0069] Of the light incident on the first liquid crystal panel 1021, the first polarization component PL1 (P wave) is transmitted through the first electrode E11 side, rotated by the first liquid crystal layer LC1 and transitioned to an S wave, and transmitted through the second electrode E12 side to be emitted, while the second polarization component PL2 (S wave) is diffused in the Y-axis direction on the first electrode E11 side, rotated by the first liquid crystal layer LC1 and transitioned to a P wave, and diffused in the X-axis direction on the second electrode E12 side to be emitted. In this way, the polarization states of the first polarization component PL1 and the second polarization component PL2 change as they pass through the first liquid crystal panel 1021, and the second polarization component PL2 is diffused in the Y-axis and X-axis directions to be emitted.

[0070] A similar phenomenon occurs at the second liquid crystal panel 1022, the third liquid crystal panel 1023, and the fourth liquid crystal panel 1024. That is, the polarization state of the first polarized component PL1 and the second polarized component PL2 incident on the second liquid crystal panel 1022 changes as they pass through the second liquid crystal panel 1022, and the first polarized component PL1 is diffused in the Y-axis and X-axis directions before being emitted. The polarization state of the first polarized component PL1 and the second polarized component PL2 incident on the third liquid crystal panel 1023 changes as they pass through the third liquid crystal panel 1023, and the second polarized component PL2 is diffused in the Y-axis and X-axis directions before being emitted. Then, the polarization state of the first polarized component PL1 and the second polarized component PL2 incident on the fourth liquid crystal panel 1024 changes as they pass through the fourth liquid crystal panel 1024, and the first polarized component PL1 is diffused in the Y-axis and X-axis directions before being emitted.

[0071] In this way, the first polarization component (P wave) of the light emitted from the light source is diffused twice in the Y-axis direction and twice in the X-axis direction as it passes through the first liquid crystal panel 1021 to the fourth liquid crystal panel 1024, and the second polarization component (S wave) is also diffused twice in the Y-axis direction and twice in the X-axis direction as it passes through the first liquid crystal panel 1021 to the fourth liquid crystal panel 1024. In other words, the first polarization component PL1 and the second polarization component PL2 are diffused evenly in the X-axis direction and the Y-axis direction, so that a rectangular light distribution pattern can be formed.

[0072] Note that the voltage application conditions shown in FIG. 7 are merely examples, and various alignment patterns can be formed by combining different voltage application conditions. For example, a line-shaped light distribution pattern can be formed by applying a voltage application pattern that diffuses the first polarization component PL1 (P wave) and the second polarization component PL2 (S wave) only in the X-axis direction or the Y-axis direction. Furthermore, a cross-shaped light distribution pattern can be formed by applying a voltage application pattern that diffuses the P-wave polarization component in the X-axis direction and the S-wave polarization component in the Y-axis direction for the first polarization component PL1 (P wave) and the second polarization component PL2 (S wave). The number of liquid crystal panels constituting the liquid crystal light control element 102 is not limited to four and can be increased. Furthermore, the overlapping manner of each liquid crystal panel can be varied. For example, the upper liquid crystal panel can be rotated at a predetermined angle relative to the lower liquid crystal panel.

[0073] In the liquid crystal light control element 102 having such a configuration and operation, the liquid crystal molecules are controlled to have a pretilt angle θp, so that even if strong light is incident from the light source and the alignment film is deteriorated, alignment disturbance of the liquid crystal layer can be suppressed, thereby improving the reliability of the liquid crystal light control device 100.

[0074] 100: Liquid crystal light control device, 102: Liquid crystal light control element, 1021: First liquid crystal panel, 1022: Second liquid crystal panel, 1023: Third liquid crystal panel, 1024: Fourth liquid crystal panel, 104: Control circuit, 106: Light source, AL11: First alignment film, AL12: Second alignment film, ALD1, ALD2: Alignment direction, E11, E21, E3 1, E41: first electrodes, E11A, E21A, E31A, E41A: first strip electrodes, E11B, E21B, E31B, E41B: second strip electrodes, E12, E22, E32, E42: second electrodes, E12A, E22A, E32A, E42A: third strip electrodes, E12B, E22B, E32B, E42B: fourth strip electrodes, LC1: first liquid crystal layer, LC2: second liquid crystal layer, LC3: third liquid crystal layer, LC4: fourth liquid crystal layer, F1: first flexible wiring board, F2: second flexible wiring board, F3: third flexible wiring board, F4: fourth flexible wiring board, PE11: first power supply line, PE12: second power supply line, PE13: third power supply line, PE14: fourth power supply line, PE15: fifth power supply line, PE16: sixth power supply line, PT11: first power supply terminal, PT12: second power supply terminal, S11, S21, S31, S41: first substrate, S12, S22, S32, S42: second substrate, T11: first connection terminal, T12: second connection terminal, T13: third connection terminal, T14: fourth connection terminal

Claims

1. A liquid crystal light control device having at least one liquid crystal panel, the at least one liquid crystal panel including: a first substrate having a first electrode including a stripe pattern and a first alignment film covering the first electrode; a second substrate having a second electrode including a stripe pattern and a second alignment film covering the second electrode; and a liquid crystal layer between the first substrate and the second substrate, wherein the liquid crystal layer has a thickness of 10 μm or more, liquid crystal molecules are twisted in an alignment from the first substrate side to the second substrate side, and a pretilt angle of the liquid crystal molecules defined by the first alignment film and the second alignment film is greater than or equal to 2 degrees and less than 8 degrees.

2. The liquid crystal light control device according to claim 1, wherein a pretilt angle of the liquid crystal molecules defined by the first alignment film and the second alignment film is between 3 degrees and 6 degrees.

3. The liquid crystal light control device according to claim 2, wherein the liquid crystal layer is made of twisted nematic liquid crystal.

4. A liquid crystal light control device as described in claim 3, wherein the longitudinal extension direction of the stripe pattern of the first electrode intersects with the longitudinal extension direction of the stripe pattern of the second electrode, and the long axis direction of the liquid crystal molecules is oriented so as to intersect with the longitudinal direction of the stripe pattern of the first electrode on the first substrate side, and is oriented so as to intersect with the longitudinal direction of the stripe pattern of the second electrode on the second substrate side.

5. A liquid crystal light control device as described in claim 4, wherein the first electrode has a plurality of first strip electrodes and second strip electrodes extending in a first direction, and the second electrode has a plurality of third strip electrodes and fourth strip electrodes extending in a second direction intersecting the first direction.

6. A liquid crystal light control device as described in claim 5, wherein the first strip electrodes and the second strip electrodes are arranged in the second direction with a center-to-center distance W, and when the thickness of the first liquid crystal layer is D, D / W is 1 or greater.

7. The liquid crystal light control device of claim 1, wherein the liquid crystal layer includes a chiral material.

8. The liquid crystal light control device according to claim 7, wherein the relationship between the thickness d of the liquid crystal layer and the pitch p of the chiral material satisfies the following: d<p / 2.

9. The liquid crystal light control device according to claim 7, wherein the relationship between the thickness d of the liquid crystal layer and the pitch p of the chiral material satisfies p / 8<d<9 / 2.

10. The liquid crystal light control device according to claim 1, wherein the at least one liquid crystal panel is made up of a plurality of liquid crystal panels, the plurality of liquid crystal panels being arranged in a stacked manner.

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