Light control device

Abstract

To provide a dimming device capable of achieving switching between a light-shielding state and a transparent state with high performance by adjusting a haze value and a polarization plane of transmitted light in a liquid crystal layer.SOLUTION: A pair of a first transparent substrate 10a and a second transparent substrate 10b which are arranged to face each other, a pair of a first transparent-electrode 11a and a second transparent-electrode 11b which are respectively attached to inner side surfaces which are facing surfaces of the respective transparent substrates 10a and 10b, and an opposing space in which the respective transparent electrodes 11a and 11b face each other, the display device includes a liquid-crystal layer (12) containing a polymer (30) and liquid-crystal molecules (21), a voltage application unit (14) that switches the liquid-crystal layer (12) between one state and another state in accordance with a voltage applied between transparent electrodes (11a, 11b), and a pair of a first polarizer (13a) and a second polarizer (13b) that are disposed on outer surfaces of the transparent substrates (10a, 10b) so as to face each other in different polarizing directions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light control device that switches between a transparent state and a light blocking state. [Background technology]

[0002] Polymer-dispersed liquid crystal elements (hereinafter referred to as PDLC) have been put to practical use as light-control elements for offices and automobiles. PDLC has the ability to switch between opaque and transparent states by switching between light scattering and light transmission, and is used in curtains, blinds, partitions, projector screens, etc.

[0003] Here, particularly for automobile sunroofs and office building windows, it is desirable for the PDLC to block excessively bright sunlight while maintaining sufficient transparency to allow for good visibility. However, while a typical PDLC can switch between scattering and transmitting light, it does not have the function of blocking transmitted light. For example, Patent Document 1 describes that by using a pair of polarizing plates, when no voltage is applied, light polarized by one polarizing plate is scattered by a mixed film, causing the polarization to be disrupted, and when this state passes through the other polarizing plate, the transmitted light appears cloudy. When a voltage is applied, the light polarized by one polarizing plate passes through the mixed film as is, preventing it from passing through the other polarizing plate and appearing black.

[0004] Furthermore, SPD elements and electrochromic elements are commonly known as light-blocking elements. Other commonly known liquid crystal molecules that can achieve light-blocking functionality include guest-host liquid crystals and TN liquid crystals. Furthermore, the inventors have proposed an element using PDLC and a dichroic dye. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-2870 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology disclosed in Patent Document 1 can block light when a voltage is applied, but when no voltage is applied, the liquid crystal becomes cloudy and cannot achieve a transparent state.

[0007] SPD elements and electrochromic elements have various problems, such as slow response speed and blue color, which limits the scope of their practical application.

[0008] Guest-host liquid crystals exhibit excellent optical properties, but because they contain a liquid, structural problems arise when they are made into films, such as dripping, leakage, and weakness to pressure and bending. Furthermore, the dichroic dyes added to the interior have poor weather resistance, making them difficult to make into films. TN liquid crystals also have light-blocking properties, but require alignment processing that is unnecessary for PDLCs, and, like guest-host liquid crystals, are difficult to make into films or enlarge.

[0009] In elements using PDLC and dichroic dye, the basic state (initial state when no voltage is applied) is cloudy due to scattering, and in order to increase the light-blocking properties, the concentration of the dichroic dye must be increased, which creates the problem of not being able to achieve sufficient contrast between the transparent and light-blocking states.

[0010] The present invention has been made to solve the above-mentioned problems, and aims to provide a dimming device that can achieve high-performance switching between a light-blocking state and a transparent state by adjusting the haze value in the liquid crystal layer and the polarization plane of transmitted light. [Means for solving the problem]

[0011] The light control device of the present invention comprises a pair of first and second transparent substrates arranged opposite each other, a pair of first and second transparent electrodes attached to the inner surfaces, which are the opposing surfaces, of the first and second transparent substrates, a liquid crystal layer formed in the opposing space between the first and second transparent electrodes and containing polymers and liquid crystal molecules, a voltage application means for switching the liquid crystal layer between one state and another state different from the one state depending on a voltage applied between the first and second transparent electrodes, and a pair of first and second polarizing elements arranged opposite each other on the outer surfaces of the first and second transparent substrates so as to have different polarization directions, and the liquid crystal layer maintains a low haze value in the one state and the other state.

[0012] In this way, in the dimming device of the present invention, polarizing elements are arranged opposite each other on the outside of the PDLC so that they have different polarization directions, and the liquid crystal layer, which changes state depending on the applied voltage, maintains a low haze value in one state and the other state, so that the liquid crystal layer is in a light-transmitting state whether in one state or the other state, and the polarizing elements act on this to transmit or block light, thereby achieving the effect of being able to switch between a transparent state and a light-blocking state (black state).

[0013] In addition, since the liquid crystal layer contains a polymer, there is no risk of dripping, making it possible to easily realize a large-sized display and a film-like display. Furthermore, the response performance, shielding performance, and weather resistance are all high, making it possible to realize a highly efficient light control device. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing the structure of a light control device according to a first embodiment of the present invention. [Figure 2] 3A to 3C are diagrams illustrating the operation of the light control device according to the first embodiment of the present invention. [Figure 3]1A and 1B are schematic diagrams showing the alignment states of liquid crystal molecules when the optical anisotropy is large and when it is small. [Figure 4] FIG. 1 is a diagram showing the relationship between the domain size of liquid crystal molecules and haze in visible light. [Figure 5] FIG. 10 is a schematic diagram illustrating an image of the structure of a liquid crystal layer in a light control device according to a second embodiment of the present invention. [Figure 6] 10A and 10B are diagrams illustrating the operation of a light control device according to a second embodiment of the present invention. [Figure 7] FIG. 10 is an explanatory diagram relating to optimization of the chiral structure in the light control device according to the second embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing experimental results regarding optimization of the chiral structure in the light control device according to the second embodiment of the present invention. [Figure 9] 6 is a schematic diagram illustrating an image of a state in which non-liquid crystal monomers are mixed in the liquid crystal layer shown in FIG. 5. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] (First embodiment of the present invention) The light control device according to this embodiment will be described with reference to Figures 1 to 4. The light control device according to this embodiment switches between a transparent state and a light-blocking state (black state) by using a PDLC, which is a polymer-dispersed liquid crystal element made by mixing polymers and liquid crystal molecules, and a polarizing element.

[0016] 1 is a schematic diagram showing the structure of a light control device according to this embodiment. The light control device 1 includes a pair of first and second transparent substrates 10a and 10b disposed opposite each other, a pair of first and second transparent electrodes 11a and 11b attached to the inner surfaces of the first and second transparent substrates 10a and 10b, a liquid crystal layer 12 formed in the space between the first and second transparent electrodes 11a and 11b and containing polymers 30 and liquid crystal molecules 21 (forming domains 20), a voltage application unit 14 that switches the liquid crystal layer 12 between one state and another state different from the one state depending on the voltage applied between the first and second transparent electrodes 11a and 11b, a control unit 15 that controls the ON / OFF of the voltage applied by the voltage application unit 14, and a pair of first and second polarizing elements 13a and 13b disposed opposite each other on the outer surfaces of the first and second transparent substrates 10a and 10b so as to have different polarization directions.

[0017] In the case of a PDLC that is generally in practical use, when the control unit 15 controls the PDLC to an OFF state in which no voltage is applied between the first transparent electrode 11a and the second transparent electrode 11b, the orientation of the liquid crystal molecules 21 in the liquid crystal layer 12 is random, resulting in a difference in the refractive index between the polymer 30 and the liquid crystal molecules 21, and the liquid crystal layer 12 becomes cloudy as incident light is diffused. On the other hand, when the control unit 15 controls the PDLC to an ON state in which a voltage is applied between the first transparent electrode 11a and the second transparent electrode 11b, the orientation of the liquid crystal molecules 21 in the liquid crystal layer 12 is aligned in a direction perpendicular to the surfaces of the first transparent substrate 10a and the second transparent substrate 10b, and the difference in the refractive index between the polymer 30 and the liquid crystal molecules 21 becomes smaller, so that the liquid crystal layer 12 transmits incident light as direct light and becomes transparent.

[0018] In the light control device 1 according to this embodiment, the haze value of the liquid crystal layer 12 is adjusted to be low, for example, to be 20% or less. In other words, unlike the general PDLC described above, the liquid crystal layer 12 maintains a transparent state (for example, a transparent state that allows at least a view through the light control device 1 to the opposite side) whether or not a voltage is applied.

[0019] The first polarizing element 13a and the second polarizing element 13b are disposed on the outer surfaces of the first transparent substrate 10a and the second transparent substrate 10b, respectively, and are disposed so that their polarization directions differ by 90 degrees. For example, the first polarizing element 13a transmits light of a first polarization, and the second polarizing element 13b transmits light of a second polarization that is different from the first polarization (e.g., 90 degrees different). That is, when randomly polarized incident light X, such as sunlight or illumination light, is incident on the light control device 1 as shown in FIG. 1, only the light of the first polarization is transmitted through the first transparent substrate 10a and the first transparent electrode 11a by the first polarizing element 13a and enters the liquid crystal layer 12. The light exiting the liquid crystal layer 12 is transmitted through the second transparent electrode 11b and the second transparent substrate 10b, and only the light of the second polarization is transmitted through the second polarizing element 13b and is emitted as output light Y.

[0020] The first polarizing element 13a and the second polarizing element 13b may be configured, for example, by a polarizing plate (including a reflective, circular, or elliptical polarizing plate), an alignment film, a polarizing filter, a combination of these with an optical compensation film such as a retardation plate, a combination of these with a heat-shielding film or other optical film, etc. Furthermore, when a display with a polarizing plate is used, the configuration may include either the first polarizing element 13a or the second polarizing element 13b.

[0021] Moreover, the first transparent substrate 10a and the second transparent substrate 10b are preferably made of a film with small retardation, such as glass, polycarbonate, cycloolefin polymer (COP), polyethersulfone (PES), or polyethylene naphthalate (PEN).

[0022] FIG. 2 is a diagram illustrating the operation of the light control device according to this embodiment. FIG. 2(A) shows the operation in the OFF state when no voltage is applied, and FIG. 2(B) shows the operation in the ON state when a voltage is applied. In FIG. 2(A), for example, assume that randomly polarized incident light X is incident. The incident light X becomes light of one polarization component (first polarization here) by passing through the first polarizing element 13a. At this time, approximately 50% of the incident light X, which is the first polarization component, is transmitted through the first polarizing element 13a. Note that in FIG. 2, the solid bidirectional arrows conceptually represent the polarization direction, and the dashed-dotted arrows conceptually represent the light propagation direction. That is, in FIG. 2(A), the incident light X that passes through the first polarizing element 13a becomes light of the first polarization, with approximately 50% of the light propagating in a straight line.

[0023] The light transmitted through the first polarizing element 13a becomes randomly polarized due to scattering and refraction caused by the optical anisotropy of the randomly oriented liquid crystal molecules 21 as it passes through the liquid crystal layer 12. However, as described above, the haze value of the liquid crystal layer 12 is low, e.g., 20% or less, so that light diffusion in the liquid crystal layer 12 is suppressed. That is, although the polarization direction of the light passing through the liquid crystal layer 12 becomes disordered and random, the direction of travel of the light tends to remain linear. Then, only the component of the other polarization (here, the second polarization, and the second polarizing element 13b is a polarizing element that transmits the second polarization) of the light emitted from the liquid crystal layer 12 passes through the second polarizing element 13b and is emitted as output light Y. Because diffusion of the light emitted from the liquid crystal layer 12 is suppressed as described above, the light has a high linearity and the light control device 1 is in a transparent state. At this time, the emitted light Y becomes light of components that account for approximately 50% of the light emitted from the liquid crystal layer 12 (when uniformly diffused by the liquid crystal layer 12).

[0024] In FIG. 2(B), for example, it is assumed that randomly polarized incident light X is incident. The incident light X becomes light of one polarized component (first polarization) by transmitting through the first polarizing element 13a. At this time, approximately 50% of the incident light X, which is the first polarized component, is transmitted through the first polarizing element 13a. In the liquid crystal layer 12, the liquid crystal molecules 21 are aligned, so the transmitted light travels straight while maintaining its polarization direction. Then, the first polarized light emitted from the liquid crystal layer 12 is blocked by the second polarizing element 13b, which transmits only second polarized light, and the light control device 1 turns black.

[0025] As described above, in the dimming device 1 according to this embodiment, the haze value in the liquid crystal layer 12 is configured to be low whether or not a voltage is applied between the first transparent electrode 11a and the second transparent electrode 11b. Therefore, by providing a first polarizing element 13a and a second polarizing element 13b on the outer surfaces of the first transparent substrate 10a and the second transparent substrate 10b so that they have different polarization directions, it is possible to achieve a transparent state and a black state (light-blocking state).

[0026] Here, a method for reducing the haze value in the liquid crystal layer 12 will be specifically described. A specific example of a method for reducing the haze value of the liquid crystal layer 12 is to use liquid crystal molecules 21 with a small optical anisotropy (Δn). FIG. 3 is a schematic diagram showing the alignment states of liquid crystal molecules when the optical anisotropy is large and when it is small. FIG. 3(A) shows liquid crystal molecules 21 with a large Δn used in a commonly known typical PDLC, and FIG. 3(B) shows liquid crystal molecules 21 with a small Δn used in this embodiment. In FIG. 3(A), the left side shows the case where the liquid crystal molecules 21 are aligned (when a voltage is applied), and the right side shows the case where the liquid crystal molecules are not aligned (when no voltage is applied). As is clear from FIG. 3(A), when the alignment is aligned, light is transmitted while maintaining its linearity due to the large Δn. However, when the alignment is not aligned, light is repeatedly scattered and refracted, resulting in a diffused state. That is, the liquid crystal layer of the PDLC that has been conventionally put into practical use is configured using liquid crystal molecules 21 with a large Δn so as to make the liquid crystal layer whiter and more opaque when no voltage is applied.

[0027] In contrast, FIG. 3(B) shows the configuration of liquid crystal molecules 21 applicable to the light control device 1 according to this embodiment. In FIG. 3(B), the left side shows the case where the liquid crystal molecules 21 are aligned (when a voltage is applied), and the right side shows the case where the liquid crystal molecules are not aligned (when no voltage is applied). As is clear from FIG. 3(B), because Δn is small, light diffusion is suppressed and light is transmitted while maintaining linearity whether the alignment is aligned or not. In other words, by using liquid crystal molecules 21 with a small optical anisotropy Δn, the haze value of the liquid crystal layer 12 is reduced, making it possible to achieve the effect shown in FIG. 2.

[0028] Another specific example of a method for reducing the haze value of the liquid crystal layer 12 is to adjust the size of the domains 20 of the liquid crystal molecules 21. FIG. 4 is a diagram showing the relationship between the domain size of the liquid crystal molecules and the haze in visible light. In the case of conventional PDLCs that are generally used in practice, it is important to make the degree of cloudiness as intense as possible (i.e., to increase the haze) when no voltage is applied. In other words, the domain size is adjusted to be near the peak of the graph in FIG. 4.

[0029] On the other hand, in the light control device 1 according to this embodiment, it is important to maintain the light as transparent as possible even when no voltage is applied (i.e., to reduce the haze). Therefore, the size of the domains 20 applied to this embodiment is set to be smaller than the minimum domain size Dmin corresponding to the haze value H, which is the standard for maintaining a cloudy state when no voltage is applied to the liquid crystal layer 12, or larger than the maximum domain size Dmax, as shown by the diagonal lines in the graph in Fig. 4. In other words, the haze value is reduced even when no voltage is applied, making it possible to achieve the effect shown in Fig. 2.

[0030] In any of the above cases, it is assumed that when a voltage is applied between first transparent electrode 11a and second transparent electrode 11b, liquid crystal layer 12 becomes transparent.

[0031] As described above, the light control device 1 according to this embodiment includes a pair of first and second transparent substrates 10a and 10b disposed opposite each other, a pair of first and second transparent electrodes 11a and 11b attached to the inner surfaces, which are the opposing surfaces of the first and second transparent substrates 10a and 10b, a liquid crystal layer 12 formed in the opposing space between the first and second transparent electrodes 11a and 11b and containing polymers 30 and liquid crystal molecules 21, and a liquid crystal layer 12 that changes color in response to a voltage applied between the first and second transparent electrodes 11a and 11b. and a pair of first polarizing elements 13a and second polarizing elements 13b arranged opposite each other on the outer surfaces of the first transparent substrate 10a and the second transparent substrate 10b so as to have different polarization directions, and the liquid crystal layer 12 maintains a low haze value in both the one state and the other state, so that the dimming device 1 can be switched between a transparent state and a black state (light-blocking state) according to the control of the voltage application unit 14 by the control unit 15.

[0032] Furthermore, since the liquid crystal layer 12 contains a mixture of polymers, it is possible to easily realize a large-sized device and a film-like device without causing dripping, etc. Furthermore, the device has high response performance, shielding performance, and weather resistance, making it possible to realize a highly efficient light control device.

[0033] Furthermore, by making the liquid crystal molecules contained in the liquid crystal layer 12 liquid crystal molecules with small optical anisotropy, or by making the domain size of the liquid crystal molecules 21 in the liquid crystal layer 12 smaller than the minimum domain size Dmin for the liquid crystal layer 12 to maintain a cloudy state, or larger than the maximum domain size Dmax for the liquid crystal layer 12 to maintain a cloudy state, the liquid crystal layer 12 can have a low haze value, and the dimming device 1 can be switched between a transparent state and a black state (light-blocking state).

[0034] (Second embodiment of the present invention) The light control device according to this embodiment will be described with reference to Fig. 5 and Fig. 6. The light control device 1 according to this embodiment realizes the function of switching between a transparent state and a black state (light-blocking state) like the light control device 1 according to the first embodiment, but has a different structure for the liquid crystal layer 12. Note that descriptions of this embodiment that overlap with those of the first embodiment will be omitted.

[0035] The liquid crystal layer 12 of the light control device 1 according to this embodiment has a structure including polymers 30 and liquid crystal molecules 21, and the liquid crystal molecules 21 have a chiral structure, which rotates the polarization direction of light passing through the liquid crystal layer 12 due to the cholesteric effect. In this case, the polymers 30 are formed using a liquid crystalline monomer as a material. That is, the liquid crystal molecules 21 have a chiral structure due to the chiral agent, and the liquid crystalline monomer is formed in a state aligned with the optical anisotropy direction of the liquid crystal molecules 21, and the polymers 30 are formed by polymerizing this liquid crystalline monomer.

[0036] FIG. 5 is a schematic diagram illustrating the structure of the liquid crystal layer in the light control device according to this embodiment. As shown in FIG. 5, the liquid crystal molecules 21 form a chiral structure due to the chiral agent, and the liquid crystal monomers are connected to each other in a fibrous form when viewed macroscopically, as indicated by the dashed-dotted line in FIG. 5. The light control device 1 shown in FIG. 5 does not have an alignment film, so the liquid crystal molecules 21 are not aligned in the plane (within a horizontal plane when the electrode plane is horizontal) on the surfaces of the first transparent electrode 11a and the second transparent electrode 11b, as indicated by the dotted line. However, when viewed microscopically near the liquid crystal molecules 21, the optical anisotropy of both the liquid crystal monomer and the liquid crystal molecules 21 are aligned in the horizontal direction (with the electrode plane being horizontal as described above). In other words, light passing through the liquid crystal layer 12 is less likely to be refracted or scattered, and the light travels in a straight line.

[0037] Furthermore, the polarization direction of light passing through liquid crystal layer 12 is rotated due to the chiral structure of liquid crystal molecules 21. The liquid crystalline monomer indicated by the dashed dotted line in Fig. 5 is cured by a polymerization process using ultraviolet light, heat, or the like to form polymer 30, and when a voltage is applied between first transparent electrode 11a and second transparent electrode 11b, only the orientation of liquid crystal molecules 21 changes.

[0038] The degree of twist of the chiral structure desirably matches the deviation of the polarization directions of the first polarizing element 13a and the second polarizing element 13b, and may be adjusted to some extent by the amount of chiral agent mixed in. For example, when the polarization directions of the first polarizing element 13a and the second polarizing element 13b are arranged with a deviation of 90 degrees, it is desirable to adjust the degree of twist to form a chiral structure with a twist rotation number of +90 degrees.

[0039] As described above, in the structure of the liquid crystal layer 12 shown in FIG. 5, the liquid crystal molecules 21 and the polymer molecules 30 are oriented in the same horizontal direction near the liquid crystal molecules 21, which makes it difficult for refraction or scattering to occur and maintains the linearity of light. That is, in the case of a typical PDLC, which is generally known, anisotropic liquid crystal molecules are mixed in a polymer with a uniform refractive index, and when the liquid crystal molecules are oriented in a direction in which the difference in refractive index is large, strong refraction and scattering occur, resulting in cloudiness. In contrast, in the liquid crystal layer 12 according to this embodiment, as described above, the liquid crystal molecules 21 and the polymer molecules 30 are oriented in the same direction, so the difference in refractive index is small when viewed from any direction, and no refraction or scattering occurs. This maintains the linearity of transmitted light, thereby achieving a transparent state.

[0040] FIG. 6 is a diagram illustrating the operation of the light control device according to this embodiment. FIG. 6(A) shows the operation in the OFF state when no voltage is applied, and FIG. 6(B) shows the operation in the ON state when a voltage is applied. In FIG. 6(A), for example, randomly polarized incident light X is incident. The incident light X becomes light of one polarization component (here, the first polarization) by passing through the first polarizing element 13a. At this time, approximately 50% of the incident light X, which is the first polarization component, is transmitted through the first polarizing element 13a. When the light that has passed through the first polarizing element 13a passes through the liquid crystal layer 12, the polarization direction of the light that has passed through the first polarizing element 13a is rotated by a predetermined angle (here, the twist rotation number + approximately 90 degrees) due to the chiral structure of the liquid crystal molecules 21 while maintaining its linearity (suppressing light that is refracted or diffused) as described above, and becomes light of another polarization component (here, the second polarization). Then, the light of the second polarized light component emitted from the liquid crystal layer 12 passes directly through the second polarizing element 13b (which is assumed to be installed with its polarization direction shifted by 90 degrees from that of the first polarizing element 13a) and is emitted as output light Y. The light emitted from the liquid crystal layer 12 has a high linearity, and the light control device 1 is in a transparent state.

[0041] In other words, in the case of Figure 2, light incident on the liquid crystal layer 12 undergoes repeated refraction and diffusion, becoming randomly polarized, and the emitted light Y that ultimately passes through the second polarizing element 13b is reduced to approximately 50% of the components of the light emitted from the liquid crystal layer 12 (if diffused evenly by the liquid crystal layer 12).However, in the case of this embodiment, the polarization direction in the liquid crystal layer 12 rotates by the torsional rotation number +90 degrees, allowing many of these components to pass through the second polarizing element 13b.

[0042] In FIG. 6(B), for example, it is assumed that randomly polarized incident light X is incident. The incident light X becomes light of one polarized light component (first polarization) by transmitting through the first polarizing element 13a. At this time, approximately 50% of the incident light X, which is the first polarized light component, is transmitted through the first polarizing element 13a. In the liquid crystal layer 12, the liquid crystal molecules 21 are aligned so that the helical structure thereof is stretched, and therefore the transmitted light travels straight while maintaining its polarization direction. In other words, the first polarized light is transmitted and emitted as is. Then, the first polarized light emitted from the liquid crystal layer 12 is blocked by the second polarizing element 13b, which transmits only the second polarized light, and the light control device 1 turns black.

[0043] Here, optimization of the chiral structure described above will be explained. When forming a chiral structure, it is desirable to satisfy two constraints in order to suppress coloring of the light control device 1. The first condition is that visible light wavelengths must be avoided in the selective reflection phenomenon (a phenomenon in which only specific wavelengths are reflected) according to the helical pitch p μm (wavelength) as shown in FIG. 7(A). If the wavelength of selective reflection were visible light, the light control device 1 would be colored. That is, it is desirable to satisfy the first condition that p is set so that λ is a wavelength longer than visible light (approximately 380 nm to 770 nm), as indicated by λ = np > 0.78 μm (n is the average refractive index of the liquid crystal molecules 21 (the average value of the ordinary refractive index no and the extraordinary refractive index ne)).

[0044] Furthermore, the second condition is that the thickness d μm of the liquid crystal layer 12 as shown in FIG. 7(B) is desirably set to an optimum value in relation to the above-mentioned pitch p so that coloring does not occur when the light passes through the first polarizing element 13a and the second polarizing element 13b.

[0045] Taking the first and second conditions into consideration, the optimal d / p value for this embodiment was determined through experiments. Fig. 8 shows the experimental results. In Fig. 8, the liquid crystal layer 20 was sandwiched between orthogonal polarizing plates and imaged with light shining from below. Fig. 8(A) shows the results of the coloring of the liquid crystal layer 20 when liquid crystal molecules 21 with a refractive index difference Δn = 0.166 were used and d / p was varied between 0.5 and 17, and Fig. 8(B) shows the results of the coloring of the liquid crystal layer 20 when liquid crystal molecules 21 with a refractive index difference Δn = 0.097 were used and d / p was varied between 1 and 13.

[0046] As shown in Figures 8(A) and 8(B), as d / p decreases, the transmission of longer wavelength (reddish) components becomes more dominant under the crossed polarizers. Gradually increasing d / p eliminates the dominance of the reddish components, and eventually the transmission of shorter wavelength (blueish) components becomes more dominant. For convenience of illustration, the experimental results are shown in grayscale. However, as shown in Figure 8, in both Figures 8(A) and 8(B), the results in the upper rows exhibit red to yellow, while the results in the lower rows exhibit white to pale blue. From these results, in Figure 8(A), appropriate coloring was observed when d / p was approximately 6 to 15, and in Figure 8(B), appropriate coloring was observed when d / p was approximately 4 to 13. In other words, in the light control device according to this embodiment, coloring was eliminated (approaching white) by setting the pitch p and the thickness d of the liquid crystal layer 12 so that d / p was approximately 4 to 15. Therefore, Δn is determined by first specifying the liquid crystal molecules 21, and the lower limit of the pitch p is determined accordingly. Once the pitch p is determined, the range of the thickness d of the liquid crystal layer 20 that optimizes coloring is determined, and the thickness d within that range can be specified.

[0047] Note that a non-liquid crystalline monomer may be further added to the structure of liquid crystal layer 12 shown in Fig. 5. Fig. 9 is a schematic diagram illustrating an image of a state in which a non-liquid crystalline monomer is mixed into the liquid crystal layer shown in Fig. 5. As shown in Fig. 9, by adding a non-liquid crystalline monomer to the extent that the chiral structure can be maintained, it is possible to strengthen the adhesive strength between first transparent electrode 11a and second transparent electrode 11b and reduce the driving voltage by voltage application unit 14.

[0048] As described above, in the dimming device of this embodiment, when no voltage is applied, the polarization direction of light passing through the liquid crystal layer 12 rotates, so that the light exiting the liquid crystal layer 12 can pass through the second polarizing element 13b, thereby increasing the transmittance.

[0049] Furthermore, since the polymer 30 is formed by polymerizing liquid crystal monomers formed in a state that aligns with the optical anisotropy direction of the liquid crystal molecules 21 arranged in a helical structure, the light passing through the liquid crystal layer 12 maintains its straightness when no voltage is applied, and the polarization direction can be rotated to pass through the second polarizing element 13b, thereby enabling a large amount of light to pass through while increasing transparency.

[0050] Furthermore, when the voltage application unit 14 applies a voltage between the first transparent electrode 11a and the second transparent electrode 11b, the orientation of the liquid crystal molecules 21 is aligned and the polarization direction of light passing through the liquid crystal layer 12 is maintained, and when no voltage is applied between the first transparent electrode 11a and the second transparent electrode 11b, the helical structure of the liquid crystal molecules 21 causes the polarization direction of light passing through the liquid crystal layer 12 to rotate in accordance with the helical structure, so that when a voltage is applied, a state of high transparency and transmittance can be achieved, and when no voltage is applied, a black (light-blocking) state can be reliably achieved.

[0051] Furthermore, the structure can be simplified by eliminating the need for an alignment film. Also, by realizing a state where there is no scattering due to PDLC, it is possible to switch between a transparent state and a black state, and it is possible to achieve high shielding properties and contrast by taking advantage of the characteristics of the first polarizing element 13a and the second polarizing element 13b.

[0052] Furthermore, the pitch p (μm) of the helical structure of the liquid crystal molecules 21 is set so that the selective reflection phenomenon in the helical structure of the liquid crystal molecules 21 avoids wavelengths of visible light, and the relationship between the pitch p (μm) and the thickness d μm of the liquid crystal layer 20 is 4≦(d / p)≦15, thereby preventing coloring in the transparent state of the liquid crystal device 1 and realizing a high-quality transparent state. [Explanation of symbols]

[0053] X incident light Y output light 1. Dimmer 10a First transparent substrate 10b 2nd transparent substrate 11a 1st transparent electrode 11b Second transparent electrode 12 Liquid crystal layer 13a First polarizing element 13b Second polarizing element 14 Voltage application section 15 Control Unit 20 domains 21 Liquid crystal molecules 30 Polymer

Claims

1. a pair of a first transparent substrate and a second transparent substrate disposed opposite to each other; a pair of a first transparent electrode and a second transparent electrode respectively attached to inner surfaces, which are opposing surfaces of the first transparent substrate and the second transparent substrate; a liquid crystal layer formed in a space where the first transparent electrode and the second transparent electrode face each other, the liquid crystal layer including a polymer and liquid crystal molecules; a voltage application means for switching the liquid crystal layer between one state and another state different from the one state in response to a voltage applied between the first transparent electrode and the second transparent electrode; a pair of first and second polarizing elements disposed opposite each other on outer surfaces of the first and second transparent substrates so as to have different polarization directions; The light control device is characterized in that the liquid crystal layer maintains a low haze value in the one state and the other state.

2. The light control device according to claim 1 , A light control device, wherein the liquid crystal molecules contained in the liquid crystal layer have small optical anisotropy.

3. The light control device according to claim 1 or 2, A light control device characterized in that the liquid crystal domain size in the liquid crystal layer is smaller than the minimum value of the liquid crystal domain size for maintaining the liquid crystal layer in a cloudy state, or is larger than the maximum value of the liquid crystal domain size for maintaining the liquid crystal layer in a cloudy state.

4. The light control device according to claim 1 , A light control device, characterized in that in either one of the one state and the other state, the polarization direction of light passing through the liquid crystal layer is rotated.

5. The light control device according to claim 4, the liquid crystal molecules have a helical structure, A light control device, characterized in that the polymer is formed by polymerizing a liquid crystalline monomer formed in a state that is aligned with the direction of optical anisotropy of the liquid crystal molecules arranged in the helical structure.

6. The light control device according to claim 5, A light control device, wherein the liquid crystal layer contains a non-liquid crystal monomer.

7. The light control device according to claim 5 or 6, when the voltage application means applies a voltage between the first transparent electrode and the second transparent electrode, the orientation of the liquid crystal molecules is aligned, and the polarization direction of light transmitted through the liquid crystal layer is maintained; A dimming device characterized in that, when no voltage is applied between the first transparent electrode and the second transparent electrode, the helical structure of the liquid crystal molecules causes the polarization direction of light passing through the liquid crystal layer to rotate in accordance with the helical structure.

8. The light control device according to claim 5 or 6, A light control device, characterized in that the pitch p (μm) of the helical structure of the liquid crystal molecules is set so that the selective reflection phenomenon in the helical structure of the liquid crystal molecules avoids wavelengths of visible light.

9. The light control device according to claim 8, A light control device, wherein the relationship between the pitch p (μm) and the thickness d (μm) of the liquid crystal layer is 4≦(d / p)≦15.

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