Dimming sheet

Abstract

To provide a liquid crystal composition for dimming sheets capable of improving responsiveness of light transmittance in low-temperature environment, and dimming sheet.SOLUTION: A dimming sheet 10A includes a liquid crystal composition 23, a dimming layer 20 having a transparent polymer layer 21 for holding the liquid crystal composition 23, and a pair of transparent electrode layers 31 and 32 sandwiching the dimming layer 20. When viscosity of the liquid crystal composition 23 at 23°C is defined as reference viscosity, a maximum value of the viscosity in a range of -20°C or more and 110°C or less is 100 times or less of the reference viscosity.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a dimming sheet.

Background Art

[0002] A dimming sheet includes a dimming layer containing a liquid crystal composition and a pair of transparent electrode layers sandwiching the dimming layer. A voltage is applied between the pair of transparent electrode layers. The light transmittance of the dimming sheet changes as the alignment state of the liquid crystal molecules changes according to the potential difference between the transparent electrode layers. For example, when the major axis direction of the liquid crystal molecules is along the thickness direction of the dimming layer, the dimming sheet is colorless and transparent, and the light transmittance of the dimming sheet is high. Further, when the major axis direction of the liquid crystal molecules intersects the thickness direction of the dimming layer, light is scattered in the dimming layer, and the light transmittance of the dimming sheet is low (see, for example, Patent Document 1). [[ID=第十三条]]

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Due to the properties of the liquid crystal composition, the responsiveness of the light transmittance of the dimming sheet to the application of voltage changes according to temperature. The wider the temperature range in which the switching of the light transmittance accompanying the application of voltage can be performed well, the more the application target of the dimming sheet can be expanded. In particular, an improvement in the responsiveness of the light transmittance in a low-temperature environment is required. For example, when a dimming sheet is applied to a window glass of a vehicle, the dimming sheet is likely to be exposed to a low-temperature environment compared to the articles inside the vehicle and the articles inside a house. If the switching of the light transmittance in a low-temperature environment can be performed quickly, the suitability of the dimming sheet for use as an in-vehicle member is enhanced.

Means for Solving the Problems

[0005] A liquid crystal composition for dimming sheets that solves the above problems is a liquid crystal composition containing liquid crystal molecules, wherein, when the viscosity of the liquid crystal composition at 23°C is taken as the reference viscosity, the maximum viscosity in the range of -20°C to 110°C is 100 times or less the reference viscosity.

[0006] According to the above configuration, even in low-temperature environments where the viscosity of the liquid crystal composition increases, the increase in viscosity of the liquid crystal composition is suppressed to the extent that a suitable change in the orientation state of the liquid crystal molecules occurs due to the application of voltage. Therefore, switching between a transparent state and an opaque state in a dimmable sheet using the liquid crystal composition is possible with good performance.

[0007] In the above configuration, the maximum viscosity may be 30 times or more the standard viscosity. According to the above configuration, the molecular weight of the liquid crystal molecules does not become too small, thus preventing the refractive index difference between the long axis and short axis in the liquid crystal molecules from becoming excessively small. Therefore, good optical properties such as haze can be obtained in the dimming sheet, and a suitable balance is struck between suppressing the viscosity of the liquid crystal composition in low-temperature environments and improving the optical properties.

[0008] In the above configuration, the maximum viscosity may be 35 times or more the reference viscosity. According to the above configuration, good haze can be easily obtained in both the transparent and opaque states of the light-adjusting sheet, which means that good optical properties can be easily obtained.

[0009] In the above configuration, the maximum viscosity is the viscosity value of the liquid crystal composition at -20°C. That's fine. With the above configuration, the viscosity at -20°C is 100 times or less of the standard viscosity, thus enabling precise improvement of the responsiveness of light transmittance in low-temperature environments.

[0010] In the above configuration, the NI point of the liquid crystal composition under atmospheric pressure may be within the range of 100°C to 145°C. With the above configuration, the NI point being 100°C or higher allows for smooth switching between the transparent and opaque states of the dimming sheet in high-temperature environments. Therefore, the dimming sheet operates well in both low-temperature and high-temperature environments, thus expanding the temperature range in which the dimming sheet can be used. Furthermore, the NI point being 145°C or lower makes it easier to keep the viscosity of the liquid crystal composition low at low temperatures.

[0011] In the above configuration, the difference in refractive index between the long axis direction and the short axis direction in the liquid crystal molecule may be 0.17 or more and 0.28 or less. According to the above configuration, a difference in refractive index of the liquid crystal molecules of 0.17 or higher allows for a good difference in haze between the transparent and opaque states of the dimming sheet. Furthermore, by keeping the difference in refractive index of the liquid crystal molecules of 0.28 or lower, the increase in molecular weight of the liquid crystal molecules is suppressed, thereby preventing the viscosity of the liquid crystal composition from becoming too high. Consequently, it is possible to suppress the difficulty in aligning the orientation of the liquid crystal molecules when their orientation changes.

[0012] In the above configuration, the liquid crystal composition may include liquid crystal molecules having a positive dielectric anisotropy. By using the liquid crystal composition with the above configuration, for example, a dimmable sheet that becomes transparent when a driving voltage is applied can be obtained.

[0013] In the above configuration, the liquid crystal composition may include liquid crystal molecules having negative dielectric anisotropy. By using the liquid crystal composition with the above configuration, for example, a dimmable sheet that becomes transparent when no driving voltage is applied can be obtained.

[0014] A light-adjusting sheet for solving the above problems comprises the above-mentioned liquid crystal composition, a light-adjusting layer having a transparent polymer layer holding the liquid crystal composition, and a pair of transparent electrode layers sandwiching the light-adjusting layer.

[0015] According to the above configuration, in a low-temperature environment, it is possible to switch well between the transparent state and the opaque state. Thereby, the suitability as an in-vehicle member in the dimming sheet is enhanced.

Effects of the Invention

[0016] According to the present invention, it is possible to enhance the responsiveness of the light transmittance in a low-temperature environment in the dimming sheet.

Brief Description of the Drawings

[0017] [Figure 1] The figure which shows the cross-sectional structure when the normal type dimming sheet in one Embodiment is in an opaque state. [Figure 2] The figure which shows the cross-sectional structure when the normal type dimming sheet in one Embodiment is in a transparent state. [Figure 3] The figure which shows the cross-sectional structure when the reverse type dimming sheet in one Embodiment is in a transparent state. [Figure 4] The figure which shows the cross-sectional structure when the reverse type dimming sheet in one Embodiment is in an opaque state.

Mode for Carrying Out the Invention

[0018] Referring to the drawings, a liquid crystal composition for a dimming sheet and an embodiment of the dimming sheet will be described. [Configuration of the Dimming Sheet] Referring to FIGS. 1 to 4, the configuration of the dimming sheet will be described. The dimming sheet of the present embodiment has, for example, a layer configuration of either a normal type or a reverse type. First, referring to FIGS. 1 and 2, the layer configuration of the normal type will be described.

[0019] As shown in FIG. 1, the normal type dimming sheet 10A includes a dimming layer 20, a first transparent electrode layer 31, a second transparent electrode layer 32, a first transparent support layer 41, and a second transparent support layer 42. The dimming layer 20 is sandwiched between the first transparent electrode layer 31 and the second transparent electrode layer 32 and is in contact with these transparent electrode layers 31, 32. The first transparent support layer 41 supports the first transparent electrode layer 31 on the side opposite to the dimming layer 20 with respect to the first transparent electrode layer 31, and the second transparent support layer 42 supports the second transparent electrode layer 32 on the side opposite to the dimming layer 20 with respect to the second transparent electrode layer 32.

[0020] The dimming layer 20 includes a transparent polymer layer and a liquid crystal composition. The transparent polymer layer has domains that are voids filled with the liquid crystal composition, and the liquid crystal composition is held within these domains.

[0021] The structure of the transparent polymer layer and the holding pattern of the liquid crystal composition are any one selected from the group consisting of polymer network type, polymer dispersion type, and capsule type. The polymer network type dimming layer 20 includes a polymer network having a three-dimensional network structure. The polymer network is an example of the transparent polymer layer, and the liquid crystal composition is held in the interconnected network-like voids in the polymer network. The polymer dispersion type dimming layer 20 includes a transparent polymer layer that defines a large number of isolated voids, and the liquid crystal composition is held in the voids dispersed in the transparent polymer layer. The capsule type dimming layer 20 holds the liquid crystal composition in the voids within the capsules dispersed in the transparent polymer layer.

[0022] In the drawings, the polymer network type dimming layer 20 is illustrated. As shown in FIG. 1, the dimming layer 20 includes a polymer network 21 and a liquid crystal composition 23. Polymer network 21 is a polymer of UV-polymerizable compounds. UV-polymerizable compounds include, for example, acrylate compounds such as butyl ethyl acrylate and cyclohexyl acrylate, methacrylate compounds such as N,N-dimethylaminoethyl methacrylate and phenoxyethyl methacrylate, stilbene compounds, diacrylate compounds, dimethacrylate compounds, triacrylate compounds, tetraacrylate compounds, trimethacrylate compounds, tetramethacrylate compounds, and oligomers of each compound.

[0023] The polymer network 21 partitions multiple domains 22. Each domain 22 is a void connecting to other adjacent domains 22. The liquid crystal composition 23 contains multiple liquid crystal molecules 24 and fills the domains 22. The liquid crystal molecules 24 are, for example, liquid crystal molecules with positive dielectric anisotropy, that is, the dielectric constant in the long axis direction of the liquid crystal molecule 24 is greater than the dielectric constant in the short axis direction of the liquid crystal molecule 24. The mass of the polymer network 21 relative to the total mass of the light-adjusting layer 20 is preferably 20% to 80%.

[0024] Each of the first transparent electrode layer 31 and the second transparent electrode layer 32 is conductive and transparent to visible light. The materials for the transparent electrode layers 31 and 32 are, for example, indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, poly(3,4-ethylenedioxythiophene), etc.

[0025] The first transparent support layer 41 and the second transparent support layer 42 are each substrates that are transparent to visible light. The materials of the transparent support layers 41 and 42 are, for example, synthetic resins and inorganic compounds. Examples of synthetic resins include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polycarbonates, and polyolefins. Examples of inorganic compounds include silicon dioxide, silicon oxynitride, and silicon nitride.

[0026] A driving voltage, which is a voltage for changing the orientation state of the liquid crystal molecules 24, is applied to the first transparent electrode layer 31 and the second transparent electrode layer 32. The dimming sheet switches from one transparent state to one opaque state based on the change in the orientation state of the liquid crystal molecules 24. The transparent state is a state in which the light transmittance, i.e., the parallel light transmittance, is relatively high, and the opaque state is a state in which the light transmittance is relatively low. Also, the transparent state is a state in which the haze is relatively low, and the opaque state is a state in which the haze is relatively high.

[0027] Figure 1 shows the opaque dimming sheet 10A. When no driving voltage is applied, the orientation of the liquid crystal molecules 24 along the long axis is irregular. Therefore, light incident on the dimming sheet 10A is scattered in various directions in the dimming layer 20. Consequently, the normal type dimming sheet 10A becomes opaque when no driving voltage is applied. The opaque dimming sheet 10A appears, for example, as a cloudy white.

[0028] Figure 2 shows the dimmable sheet 10A in a transparent state. When the dielectric anisotropy of the liquid crystal molecules 24 is positive, when a driving voltage is applied, the liquid crystal molecules 24 are oriented so that their long axis is aligned with the electric field direction. That is, the orientation of the liquid crystal molecules 24 changes so that their long axis is aligned with the thickness direction of the dimmable layer 20. As a result, light scattering in the dimmable layer 20 is suppressed, and light is more easily transmitted through the dimmable sheet 10A. Therefore, the normal type dimmable sheet 10A becomes transparent when a driving voltage is applied.

[0029] The polymer network type light-adjusting layer 20 is formed by irradiating a coating film, which consists of a mixture of an ultraviolet polymerizable compound and a liquid crystal composition 23 for forming a polymer network 21, with ultraviolet light. Specifically, the coating film is sandwiched between a laminate of a first transparent electrode layer 31 and a first transparent support layer 41, and a laminate of a second transparent electrode layer 32 and a second transparent support layer 42, and by irradiating the coating film with ultraviolet light through these laminates, a normal type light-adjusting sheet 10A having a polymer network type light-adjusting layer 20 is formed.

[0030] Next, with reference to Figures 3 and 4, the layer structure of the reverse-type dimming sheet will be described. As shown in Figure 3, the reverse-type dimming sheet 10B comprises a dimming layer 20, transparent electrode layers 31, 32, and transparent support layers 41, 42, in addition to a first orientation layer 51 and a second orientation layer 52. The first orientation layer 51 is located between the dimming layer 20 and the first transparent electrode layer 31 and is in contact with these layers. The second orientation layer 52 is located between the dimming layer 20 and the second transparent electrode layer 32 and is in contact with these layers.

[0031] The first alignment layer 51 and the second alignment layer 52 regulate the orientation of the liquid crystal molecules 24. The alignment layers 51 and 52 are, for example, vertical alignment films. The vertical alignment films orient the liquid crystal molecules 24 so that their long axis is aligned with the thickness direction of the dimming layer 20. When the alignment layers 51 and 52 are vertical alignment films, the liquid crystal molecules 24 used are liquid crystal molecules with negative dielectric anisotropy, that is, liquid crystal molecules in which the dielectric constant in the long axis direction is smaller than the dielectric constant in the short axis direction.

[0032] The materials for the orientation layers 51 and 52 are, for example, polyimide, polyamide, and polyvinyl alcohol. These include organic compounds such as cyanide compounds, inorganic compounds such as silicon oxide and zirconium oxide, and silicones. Orientation treatments for forming the orientation layers 51 and 52 include, for example, rubbing treatment, polarized irradiation treatment, and microfabrication treatment.

[0033] Figure 3 shows the dimming sheet 10B in a transparent state. When no driving voltage is applied, the liquid crystal molecules 24 are oriented so that their long axis is aligned with the thickness direction of the dimming layer 20 due to the orientation restricting force from the alignment layers 51 and 52. As a result, light scattering in the dimming layer 20 is suppressed, and light is more easily transmitted through the dimming sheet 10B. Therefore, the reverse-type dimming sheet 10B becomes transparent when a driving voltage is applied.

[0034] Figure 4 shows the opaque state of the dimming sheet 10B. When the dielectric anisotropy of the liquid crystal molecules 24 is negative, when a driving voltage is applied, the liquid crystal molecules 24 are oriented so that their long axis is perpendicular to the electric field direction. That is, the orientation of the liquid crystal molecules 24 changes so that their long axis intersects the thickness direction of the dimming layer 20. As a result, light scattering is more likely to occur in the dimming layer 20. Therefore, the reverse-type dimming sheet 10B becomes opaque when a driving voltage is applied.

[0035] The reverse-type dimmable sheet 10B, which has a polymer network-type dimmable layer 20, is formed by sandwiching the aforementioned coating film between a laminate of a first orientation layer 51, a first transparent electrode layer 31, and a first transparent support layer 41, and a laminate of a second orientation layer 52, a second transparent electrode layer 32, and a second transparent support layer 42, and irradiating the coating film with ultraviolet light through these laminates.

[0036] The layer configuration of the dimming sheet is not limited to the above, as long as it is configured to switch between a transparent state and an opaque state based on the change in the orientation state of the liquid crystal molecules due to the application of a driving voltage. For example, the dimming sheet may include a polarizing layer that controls the polarization of incident or transmitted light to the dimming layer 20, and the alignment layers 51 and 52 may be horizontal alignment films. Whether the dimming sheet becomes transparent or opaque when a driving voltage is applied can be changed by the presence or absence of the alignment layers 51 and 52, the direction in which the orientation restricting force by the alignment layers 51 and 52 acts, the positive or negative dielectric anisotropy of the liquid crystal molecules, the presence or absence of a polarizing layer, etc.

[0037] At least one of the front and back surfaces of the dimming sheet is attached to a transparent plate made of glass, resin, or the like. The transparent plate is, for example, a windowpane in various buildings, a partition installed indoors, or a windowpane or windshield in a moving object such as a vehicle or aircraft. The surface of the transparent plate may be flat or curved. The dimming sheet of this embodiment uses a liquid crystal composition that has the characteristic of switching well between a transparent state and an opaque state in a low-temperature environment, and is therefore suitably used in automotive components that are required to be usable in low-temperature environments. In other words, the dimming sheet of this embodiment is suitable for application to the windowpanes of vehicles.

[0038] [Properties of liquid crystal compositions] The properties of the liquid crystal composition used in the dimming sheet of this embodiment will be described in detail. The main component of the liquid crystal composition is a liquid crystal molecule. The liquid crystal molecule is selected from the group consisting of, for example, Schiff bases, azos, azoxys, biphenyls, terphenyls, benzoic acid esters, trans, pyrimidines, pyridazines, cyclohexanecarboxylic acid esters, phenylcyclohexanes, biphenylcyclohexanes, dicyanobenzenes, naphthalenes, and dioxanes. The liquid crystal composition may contain only one type of liquid crystal molecule or may contain multiple types of liquid crystal molecules. The liquid crystal composition has a nematic phase at room temperature.

[0039] The liquid crystal composition may contain components other than liquid crystal molecules. These components other than liquid crystal molecules may include, for example, viscosity reducers, dichroic dyes, defoamers, antioxidants, UV absorbers, and weather stabilizers. Therefore, in order to obtain good anisotropy of the liquid crystal composition and good optical properties of the dimming sheet such as light transmittance and haze, it is preferable that the total mass ratio of liquid crystal molecules in the liquid crystal composition is 80% or more of the total mass of the liquid crystal composition.

[0040] The viscosity of the liquid crystal composition changes with temperature, increasing as the temperature decreases. If the viscosity of the liquid crystal composition is too high in a low-temperature environment, the liquid crystal molecules become less mobile, making it difficult for the orientation of the liquid crystal molecules to change in response to the application of a driving voltage. As a result, the responsiveness of the light transmittance in the dimming sheet decreases, meaning that it takes time to switch between the transparent and opaque states, or it may not be possible to switch at all. In the dimming layer 20, as described above, the liquid crystal molecules change orientation within minute domains partitioned within the transparent polymer layer. Therefore, compared to structures where the liquid crystal composition is filled in a wide layered area, such as liquid crystal panels used in display devices, the viscosity of the liquid crystal composition has a greater effect on the ease with which the orientation of the liquid crystal molecules changes, and the responsiveness of the light transmittance tends to be low in low-temperature environments.

[0041] The viscosity of a liquid crystal composition changes nonlinearly with respect to temperature, increasing rapidly as the temperature decreases. Furthermore, the degree of viscosity increase from room temperature to low temperatures varies depending on the composition of the liquid crystal composition. Therefore, the inventors of this application have found that by using the viscosity at room temperature (23°C) as a reference, they can calculate the degree of change in viscosity of the liquid crystal composition at low and high temperatures, and by using these calculation results, it is possible to evaluate the responsiveness of the light transmittance of a dimming sheet at temperatures other than room temperature.

[0042] In other words, if the maximum viscosity Vm of the liquid crystal composition in the range of -20°C to 110°C is 100 times or less the reference viscosity Vb of the liquid crystal composition at 23°C, then the switching between the transparent and opaque states of the dimming sheet can be performed smoothly within the above temperature range. As mentioned above, the viscosity of the liquid crystal composition increases as the temperature decreases, so the maximum viscosity Vm is the viscosity in the low-temperature region, specifically the viscosity at -20°C.

[0043] The reference viscosity Vb is, for example, between 10 mPa·s and 500 mPa·s. If the reference viscosity Vb is within the above range, the switching between the transparent and opaque states of the dimming sheet can be done quickly at 23°C, and because the maximum viscosity Vm is 100 times or less of the reference viscosity Vb, the switching between the transparent and opaque states can be done at a speed close to that at room temperature even in a low-temperature environment. For example, the switching between the transparent and opaque states can be completed within 60 seconds from the start of application of the drive voltage. The viscosity of the liquid crystal composition is measured, for example, using a viscometer (VM-300) manufactured by Sekonic Corporation, in accordance with JIS Z 8809:2011.

[0044] The reference viscosity Vb and maximum viscosity Vm of a liquid crystal composition can be adjusted by the type of liquid crystal molecules contained in the composition, and by the presence or absence and amount of viscosity-reducing agent added to the liquid crystal composition. Viscosity-reducing agents have the function of reducing the viscosity of the liquid crystal composition. In particular, by using a plasticizer as the viscosity-reducing agent, which improves low-temperature flexibility by suppressing solidification of the liquid crystal composition, the ratio of maximum viscosity Vm to reference viscosity Vb can be reduced. As such a viscosity-reducing agent, for example, an alkenyl compound shown in the following structural formula (1) can be used. In order to obtain good anisotropy of the liquid crystal composition and optical properties of the dimming sheet, it is preferable that the content of the viscosity-reducing agent in the liquid crystal composition is 10% or less of the total mass of the liquid crystal composition. [ka] Furthermore, by adding a chiral agent that imparts twisting to the liquid crystal molecules to the liquid crystal composition, The viscosity of the resulting product can also be finely adjusted.

[0045] Furthermore, the NI point (Nematic-Isotropic transition temperature) of the liquid crystal composition under atmospheric pressure is preferably between 100°C and 145°C. Since the liquid crystal composition loses its anisotropy at temperatures above the NI point, if the NI point is too low, the liquid crystal molecules will not align well in high-temperature environments, making it difficult to switch between the transparent and opaque states of the dimming sheet. If the NI point is 100°C or higher, the orientation of the liquid crystal molecules will change well even in high-temperature environments, and the switching between the transparent and opaque states will be smooth.

[0046] On the other hand, the higher the NI point, the greater the viscosity of the liquid crystal composition at low temperatures. If the NI point is 145°C or lower, it is possible to suppress the increase in the maximum viscosity Vm of the liquid crystal composition. As mentioned above, it is possible to reduce the viscosity of the liquid crystal composition at low temperatures by adding viscosity-reducing agents, but if the proportion of non-liquid crystal molecules in the liquid crystal composition increases, there are concerns about the anisotropy of the liquid crystal composition and the deterioration of the optical properties of the dimming sheet. If the NI point is 145°C or lower, the viscosity of the liquid crystal composition at low temperatures can be kept low, so that the maximum viscosity Vm can be kept to 100 times or less of the reference viscosity Vb without adding an excessive amount of viscosity-reducing agent.

[0047] Next, we will explain the properties of the liquid crystal composition that affect the optical properties of the dimming sheet. In the transparent state of the dimmable sheet, it is preferable that the visual recognition of objects through the dimmable sheet is clearer, i.e., that haze is small. On the other hand, in the opaque state of the dimmable sheet, it is preferable that the visual recognition of objects through the dimmable sheet is more difficult, i.e., that haze is large. Therefore, it is preferable that the difference in haze between the transparent and opaque states is large. The haze is measured in accordance with JIS K 7136:2000.

[0048] The larger the refractive index difference Δn (Δn = anomalous refractive index ne - ordinary refractive index no) between the long axis and short axis of the liquid crystal molecule, the greater the difference in refractive index of the liquid crystal molecule with respect to incident light on the dimming layer 20 between when a driving voltage is applied and when it is not, resulting in a larger difference in light scattering. Therefore, the difference in haze between the transparent state and the opaque state becomes larger. To obtain a good difference in haze between the transparent state and the opaque state, it is preferable that the refractive index difference Δn is 0.17 or greater.

[0049] On the other hand, the larger the refractive index difference Δn of the liquid crystal molecules, the larger the molecular weight of the liquid crystal molecules tends to be, and the larger the molecular weight of the liquid crystal molecules, the less mobile they become. Therefore, the larger the refractive index difference Δn of the liquid crystal molecules, the higher the viscosity of the liquid crystal composition at low temperatures, and the less likely the orientation state is to change. Also, even at room temperature, the orientation becomes less likely to align when a driving voltage is applied, so the optical properties after the change in orientation state tend to be lower. To improve the responsiveness of light transmittance and the optical properties in low-temperature environments, it is preferable that the refractive index difference Δn is 0.28 or less.

[0050] Conversely, a low viscosity of the liquid crystal composition at low temperatures means that the molecular weight of the liquid crystal molecules is small and the refractive index difference Δn is small. In other words, if the maximum viscosity Vm is excessively small, the refractive index difference Δn becomes too small, which leads to a decrease in the optical properties of the dimming sheet. Therefore, in order to ensure a refractive index difference Δn that provides a good difference in haze between the transparent and opaque states, it is preferable that the maximum viscosity Vm is 30 times or more the reference viscosity Vb, and more preferably that the maximum viscosity Vm is 35 times or more the reference viscosity Vb.

[0051] Furthermore, if the liquid crystal composition contains multiple types of liquid crystal molecules, the refractive index difference Δn is the difference between the average value of the refractive indices along the long axis of the multiple types of liquid crystal molecules and the average value of the refractive indices along the short axis of the multiple types of molecules.

[0052] [Examples] The liquid crystal composition and dimming sheet described above will be explained using specific examples and comparative examples.

[0053] (Liquid crystal composition) Twelve liquid crystal compositions, Examples 1-9 and Comparative Examples 1-3, were prepared using seven liquid crystal materials from Merck (MLC-6608, MLC-6609, MLC-6610, MLC-3018, ZLI-2806, ZLI-1131, ZLI-1132). The twelve liquid crystal compositions consist of one or more of the above seven liquid crystal materials and have different compositions from each other. In addition, an alkenyl compound shown in structural formula (1) above was added to some of the liquid crystal compositions as a viscosity-reducing agent, so that its concentration in the liquid crystal composition was 5% by mass.

[0054] (Dimmable sheet) Using the liquid crystal compositions of each example and comparative example, normal-type dimmable sheets equipped with a polymer network type dimmable layer were prepared. Specifically, a coating solution was prepared by mixing an acrylic monomer, which is an ultraviolet polymerizable compound, with the liquid crystal composition. The coating solution was then applied to a first transparent electrode layer supported by a first transparent support layer to form a coating film. The first transparent electrode layer, supported by a second transparent support layer, was placed on top of the coating film, and these laminates were irradiated with ultraviolet light. As a result, the acrylic monomer in the coating film polymerized to form a polymer network, and a dimmable layer in which the liquid crystal composition was held within the polymer network was formed. The refractive index of the polymer network is 1.5. The material of each transparent electrode layer is indium tin oxide, and the material of each transparent support layer is polyethylene terephthalate. The manufacturing conditions, such as the ultraviolet exposure conditions, were set for each example and comparative example to minimize the haze in the transparent state of the dimmable sheet.

[0055] (Evaluation method) [Viscosity change] The viscosity of the liquid crystal compositions of each example and comparative example was measured at -20°C, 0°C, 23°C, 90°C, and 110°C. Viscosity was measured using a Sekonic viscometer (VM-300) in accordance with JIS Z 8809:2011. The viscosity at 23°C was then used as the reference viscosity Vb, and the ratios of the viscosities at -20°C, 0°C, 90°C, and 110°C to the reference viscosity Vb were calculated.

[0056] [Responsiveness of light transmittance] For each example and comparative example of the dimming sheet, the responsiveness of the light transmittance was evaluated by determining whether it could be driven at -20°C and 90°C. Specifically, it was determined that the sheet could be driven if the switch from opaque to transparent state was completed within 60 seconds of starting to apply the drive voltage to the dimming sheet. Completion of the switch from opaque to transparent state means that the change in haze is complete. At 23°C, all dimming sheets in each example and comparative example were able to be driven.

[0057] [Optical properties] For each example and comparative example of the dimming sheet, the haze was measured in both the transparent and opaque states at 23°C. The haze was measured using a haze meter (NDH7000) manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS K 7136:2000.

[0058] (Evaluation results) Table 1 shows the presence or absence of viscosity-reducing agents added to the liquid crystal compositions of each example and comparative example. The viscosity at 23°C without the addition of a viscosity-reducing agent and the viscosity at 23°C after the addition of a viscosity-reducing agent are shown.

[0059] Table 2 shows the ratio of viscosity Vb to reference viscosity Vb at -20°C, 0°C, 90°C, and 110°C, the NI point, and the refractive index difference Δn of the liquid crystal molecules for each example and comparative example of the liquid crystal composition. The reference viscosity Vb for the examples and comparative examples with added viscosity reducers is the viscosity at 23°C after the addition of the viscosity reducer. Furthermore, Table 2 shows the results of the determination of whether each example and comparative example can be driven on the dimming sheet, and the haze measurement results.

[0060] [Table 1]

[0061] [Table 2]

[0062] As shown in Table 2, the viscosity of the liquid crystal compositions in each example and comparative example is maximum at -20°C in the range of -20°C to 110°C. In Examples 1 to 9, where the maximum viscosity Vm is 100 times or less the reference viscosity Vb, the dimming sheet could be driven at -20°C. On the other hand, in Comparative Examples 1 to 3, where the maximum viscosity Vm exceeds 100 times the reference viscosity Vb, the dimming sheet could not be driven at -20°C. Therefore, it was confirmed that good switching between transparent and opaque states is possible in low-temperature environments if the maximum viscosity Vm is 100 times or less the reference viscosity Vb.

[0063] Furthermore, in Examples 7 and 8, where the NI point was less than 100°C, the dimming sheet could not be driven at 90°C. Therefore, it was confirmed that the NI point should be 100°C or higher in order to enable good switching between transparent and opaque states in high-temperature environments.

[0064] Furthermore, in Examples 7 and 9, where the refractive index difference Δn of the liquid crystal molecules is less than 0.17, the haze in the transparent state is higher than in the others, and the haze in the opaque state is lower than in the others, resulting in a smaller difference in haze between the transparent and opaque states. Specifically, in Example 7, the difference in haze between the transparent and opaque states is smaller, particularly due to the lower haze in the opaque state. Therefore, it is suggested that refractive indices in the long and short axes exist in the region where the refractive index of the liquid crystal molecules in the opaque state is close to the refractive index of the polymer network, resulting in low light scattering in the light-adjusting layer in the opaque state. On the other hand, in Example 9, the difference in haze between the transparent and opaque states is smaller, particularly due to the higher haze in the transparent state. Therefore, it is suggested that refractive indices in the long and short axes exist in the region where the refractive index of the liquid crystal molecules in the transparent state is far from the refractive index of the polymer network, resulting in light scattering in the light-adjusting layer even in the transparent state.

[0065] Furthermore, in Comparative Example 3, where the refractive index difference Δn exceeds 0.28, the haze in the transparent state is high. This is because the large molecular weight of the liquid crystal molecules makes it difficult for them to move, resulting in the liquid crystals remaining in place even after switching from the opaque state to the transparent state by applying the driving voltage. It is thought that the orientation of the molecules is not perfectly aligned, leaving some irregularity, which causes light scattering in the light-adjusting layer.

[0066] In contrast, in Examples 1-6, 8 and Comparative Examples 1, 2, where the refractive index difference Δn is between 0.17 and 0.28, the haze is good in both the transparent and opaque states, meaning that good optical properties are obtained.

[0067] Furthermore, Examples 7 and 9 suggest that if the maximum viscosity Vm is less than approximately 30 times the reference viscosity Vb, the refractive index difference Δn becomes too small, resulting in a decrease in optical properties as described above. As shown in Examples 1 to 6 and 8, if the maximum viscosity Vm is 35 times or more the reference viscosity Vb, the haze is good in both the transparent and opaque states, suggesting that good optical properties can be obtained.

[0068] As described above in the embodiments and examples, the liquid crystal composition and dimming sheet can provide the following effects. (1) In the liquid crystal composition, the maximum viscosity Vm in the range of -20°C to 110°C is 100 times or less the reference viscosity Vb at 23°C. As a result, even in low-temperature environments where the viscosity of the liquid crystal composition increases, the increase in viscosity of the liquid crystal composition is suppressed to the extent that a change in the orientation state of the liquid crystal molecules due to the application of a driving voltage occurs suitably. Therefore, switching between a transparent state and an opaque state in a dimmable sheet using the liquid crystal composition is possible with good performance.

[0069] (2) If the maximum viscosity Vm is 30 times or more the reference viscosity Vb, the molecular weight of the liquid crystal molecules will not become too small, thus preventing the refractive index difference Δn of the liquid crystal molecules from becoming excessively small. Therefore, good optical properties such as haze can be obtained in the dimming sheet, and a suitable balance can be struck between suppressing the viscosity of the liquid crystal composition in low-temperature environments and improving the optical properties. Furthermore, if the maximum viscosity Vm is 35 times or more the reference viscosity Vb, good haze can be easily obtained in both the transparent and opaque states of the dimming sheet, that is, good optical properties can be easily obtained.

[0070] (3) The NI point of the liquid crystal composition under atmospheric pressure is 100°C or higher, which allows for smooth switching between the transparent and opaque states of the dimming sheet in high-temperature environments. Therefore, the dimming sheet operates well in both low-temperature and high-temperature environments, which expands the temperature range in which the dimming sheet can be used. In addition, the NI point being 145°C or lower makes it easier to keep the viscosity of the liquid crystal composition low at low temperatures.

[0071] (4) When the refractive index difference Δn of the liquid crystal molecules is 0.17 or more, a good difference in haze between the transparent and opaque states of the dimming sheet can be obtained. Furthermore, when the above Δn is 0.28 or less, the molecular weight of the liquid crystal molecules is suppressed to the point where it becomes excessively large, which makes it possible to suppress the viscosity of the liquid crystal composition in low-temperature environments and to suppress the difficulty in aligning the orientation of the liquid crystal molecules when the orientation state of the liquid crystal molecules changes. Therefore, it is possible to improve the responsiveness of light transmittance in low-temperature environments and the optical properties of the dimming sheet.

[0072] (5) By using a liquid crystal composition in which the dielectric anisotropy of the liquid crystal molecules is positive, for example, a dimmable sheet can be obtained that becomes transparent when a driving voltage is applied. Alternatively, by using a liquid crystal composition in which the dielectric anisotropy of the liquid crystal molecules is negative, for example, a dimmable sheet can be obtained that becomes opaque when a driving voltage is applied.

[0073] (6) By providing the dimming sheet with a dimming layer 20 having a transparent polymer layer holding the above liquid crystal composition, the dimming sheet can be switched smoothly between a transparent state and an opaque state in a low-temperature environment. This enhances the suitability of the dimming sheet as an automotive component. . [Explanation of Symbols]

[0074] 10A, 10B… Dimmable sheet 20…Dimming layer 21…Polymer Network 22…domain 23…Liquid crystal composition 24…Liquid crystal molecules 31,32...Transparent electrode layer 41,42...Transparent support layer 51, 52… Orientation layers

Claims

1. A light-adjusting layer having a liquid crystal composition containing liquid crystal molecules and a viscosity-reducing agent, and a transparent polymer layer that holds the liquid crystal composition, The light-adjusting layer is sandwiched between a pair of transparent electrode layers, The mass ratio of the transparent polymer layer in the light-adjusting layer is 20% or more and 80% or less. When the viscosity of the liquid crystal composition at 23°C is taken as the reference viscosity, the maximum viscosity in the range of -20°C to 110°C is 100 times or less the reference viscosity, and is 696 mPa·s to 7275 mPa·s. The NI point of the liquid crystal composition under atmospheric pressure is located in the range of 125°C to 145°C. The difference in refractive index between the long axis and the short axis in the liquid crystal molecule is 0.20 or more and 0.28 or less. The liquid crystal composition contains, as the viscosity reducing agent, a compound represented by the following formula (1). Dimming sheet. 【Chemistry 1】

2. The maximum value of the viscosity is 30 times or more the standard viscosity. The dimming sheet according to claim 1.

3. The maximum value of the viscosity is 35 times or more the standard viscosity. The dimming sheet according to claim 2.

4. The maximum viscosity value is the viscosity value of the liquid crystal composition at -20°C. A dimming sheet according to any one of claims 1 to 3.

5. The liquid crystal composition contains the liquid crystal molecules having positive dielectric anisotropy. A dimming sheet according to any one of claims 1 to 4.

6. The liquid crystal composition includes the liquid crystal molecules having negative dielectric anisotropy. A dimming sheet according to any one of claims 1 to 4.

7. The light-adjusting layer is sandwiched between the light-adjusting layer and the pair of transparent electrode layers by a pair of orientation layers. The dimming sheet according to claim 6.

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