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 light controlling sheet. [Background technology]

[0002] The light-adjusting sheet comprises a light-adjusting layer containing a liquid crystal composition and a pair of transparent electrode layers sandwiching the light-adjusting layer. A voltage is applied between the pair of transparent electrode layers. The orientation state of the liquid crystal molecules changes depending on the potential difference between the transparent electrode layers, thereby changing the light transmittance of the light-adjusting sheet. For example, when the long axis direction of the liquid crystal molecules is along the thickness direction of the light-adjusting layer, the light-adjusting sheet is colorless and transparent, and the light transmittance of the light-adjusting sheet is high. On the other hand, when the long axis direction of the liquid crystal molecules intersects with the thickness direction of the light-adjusting layer, light is scattered within the light-adjusting layer, and the light transmittance of the light-adjusting sheet is low (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-45135 A Summary of the Invention [Problem to be solved by the invention]

[0004] Due to the properties of the liquid crystal composition, the responsiveness of the light transmittance of the light control sheet to the application of a voltage varies depending on the temperature. The wider the temperature range in which the light transmittance can be switched well with the application of a voltage, the more the light control sheet can be applied, and there is a particular demand for improved light transmittance responsiveness in low-temperature environments. For example, when a light control sheet is applied to the window glass of a vehicle, the light control sheet is more likely to be exposed to low-temperature environments than items inside the vehicle or items indoors. If the light transmittance can be switched quickly in low-temperature environments, the suitability of the light control sheet for use as an in-vehicle component is improved. [Means for solving the problem]

[0005] A liquid crystal composition for a light-adjusting sheet that solves the above problem is a liquid crystal composition containing liquid crystal molecules, and when the viscosity of the liquid crystal composition at 23°C is taken as a reference viscosity, the maximum value of the viscosity in the range of -20°C to 110°C is 100 times or less of the reference viscosity.

[0006] According to the above-mentioned configuration, even in a low-temperature environment where the viscosity of the liquid crystal composition increases, the increase in viscosity of the liquid crystal composition is suppressed to a degree that favorably causes a change in the alignment state of the liquid crystal molecules due to the application of a voltage, and therefore, the light control sheet using the liquid crystal composition can be satisfactorily switched between a transparent state and an opaque state.

[0007] In the above configuration, the maximum value of the viscosity may be 30 times or more the reference viscosity. According to the above-mentioned configuration, since the molecular weight of the liquid crystal molecules is not too small, the refractive index difference between the long axis direction and the short axis direction of the liquid crystal molecules is prevented from becoming too small. Therefore, the optical properties such as haze of the light control sheet can be obtained well, and a good balance is achieved between suppressing the viscosity of the liquid crystal composition in a low temperature environment and improving the optical properties.

[0008] In the above configuration, the maximum value of the viscosity may be 35 times or more the reference viscosity. According to the above configuration, it becomes easier to obtain a good haze in both the transparent and opaque states of the light controlling sheet, that is, it becomes easier to obtain good optical characteristics.

[0009] In the above configuration, the maximum viscosity is a viscosity value of the liquid crystal composition at −20° C. may be also possible. According to the above configuration, since the viscosity at -20°C is 100 times or less the reference viscosity, it is possible to accurately improve the responsiveness of the light transmittance in a low temperature environment.

[0010] In the above configuration, the NI point of the liquid crystal composition under atmospheric pressure may be in the range of 100° C. or higher and 145° C. or lower. According to the above configuration, since the NI point is 100°C or higher, the light-adjusting sheet can be switched between a transparent state and an opaque state in a high-temperature environment. Therefore, the light-adjusting sheet operates well in both low-temperature and high-temperature environments, and the temperature range in which the light-adjusting sheet can be used can be expanded. In addition, since the NI point is 145°C or lower, it is easy to keep the viscosity of the liquid crystal composition low at low temperatures.

[0011] In the aforementioned configuration, the difference in refractive index between the major axis direction and the minor axis direction of the liquid crystal molecules may be 0.17 or more and 0.28 or less. According to the above configuration, since the refractive index difference of the liquid crystal molecules is 0.17 or more, a good difference in haze between the transparent state and the opaque state of the light control sheet can be obtained. Also, since the refractive index difference of the liquid crystal molecules is 0.28 or less, the molecular weight of the liquid crystal molecules is prevented from increasing, and the viscosity of the liquid crystal composition is prevented from becoming too high, and therefore, it is possible to prevent the liquid crystal molecules from becoming difficult to align when the orientation state of the liquid crystal molecules changes.

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

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

[0014] A light control sheet for solving the above problem includes the above liquid crystal composition, a light control layer having a transparent polymer layer that holds the liquid crystal composition, and a pair of transparent electrode layers that sandwich the light control layer.

[0015] According to the above-mentioned configuration, it is possible to satisfactorily switch between a transparent state and an opaque state in a low-temperature environment, which enhances the suitability of the light controlling sheet as an in-vehicle member. Effect of the Invention

[0016] According to the present invention, the responsiveness of the light transmittance of the light controlling sheet in a low temperature environment can be improved. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a diagram showing a cross-sectional structure of a normal-type light adjusting sheet in an embodiment when it is in an opaque state. [Diagram 2] FIG. 2 is a diagram showing a cross-sectional structure of a normal-type light adjusting sheet in one embodiment when it is in a transparent state. [Diagram 3] FIG. 2 is a diagram showing a cross-sectional structure of a reverse-type light controlling sheet in an embodiment when it is in a transparent state. [Figure 4] FIG. 2 is a diagram showing a cross-sectional structure of a reverse-type light controlling sheet in an embodiment when it is in an opaque state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An embodiment of a liquid crystal composition for a light controlling sheet and a light controlling sheet will be described with reference to the drawings. [Composition of light control sheet] The structure of the light controlling sheet will be described with reference to Fig. 1 to Fig. 4. The light controlling sheet of the present embodiment has, for example, either a normal type or a reverse type layer structure. First, the layer structure of the normal type will be described with reference to Fig. 1 and Fig. 2.

[0019] 1, the normal-type light-controlling sheet 10A includes a light-controlling 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 light-controlling 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 and 32. The first transparent support layer 41 supports the first transparent electrode layer 31 on the side opposite the light-controlling 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 the light-controlling layer 20 with respect to the second transparent electrode layer 32.

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

[0021] The structure of the transparent polymer layer and the holding type of the liquid crystal composition are any one selected from the group consisting of a polymer network type, a polymer dispersion type, and a capsule type. The polymer network type light control layer 20 has a polymer network having a three-dimensional mesh shape. The polymer network is an example of a transparent polymer layer, and the liquid crystal composition is held in the interconnected mesh-like voids in the polymer network. The polymer dispersion type light control layer 20 has a transparent polymer layer that partitions 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 light control layer 20 holds the liquid crystal composition in the voids in capsules dispersed in the transparent polymer layer.

[0022] The drawing illustrates a polymer network type light control layer 20. As shown in FIG. 1, the light control layer 20 includes a polymer network 21 and a liquid crystal composition 23. The polymer network 21 is a polymer of an ultraviolet-polymerizable compound. Examples of the ultraviolet-polymerizable compound include 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 defines a plurality of domains 22. Each domain 22 is a gap that is connected to adjacent domains 22. The liquid crystal composition 23 includes a plurality of liquid crystal molecules 24 and fills the domains 22. The liquid crystal molecules 24 are, for example, liquid crystal molecules having a positive dielectric anisotropy, that is, the dielectric constant of the liquid crystal molecules 24 in the long axis direction is greater than the dielectric constant of the liquid crystal molecules 24 in the short axis direction. The mass of the polymer network 21 relative to the total mass of the light-switching layer 20 is preferably 20% or more and 80% or less.

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

[0025] Each of the first transparent support layer 41 and the second transparent support layer 42 is a base material that is transparent to light in the visible region. The material of the transparent support layers 41 and 42 is, for example, a synthetic resin or an inorganic compound. Examples of the synthetic resin include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polycarbonates, polyolefins, etc. Examples of the inorganic compound include silicon dioxide, silicon oxynitride, silicon nitride, etc.

[0026] A driving voltage is applied to the first transparent electrode layer 31 and the second transparent electrode layer 32, which is a voltage for changing the alignment state of the liquid crystal molecules 24. The light control sheet switches from one of a transparent state and an opaque state to the other based on the change in the alignment 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. In addition, 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] FIG. 1 shows the light-adjusting sheet 10A in an opaque state. When no driving voltage is applied, the orientation of the long axis direction of the liquid crystal molecules 24 is irregular. Therefore, light incident on the light-adjusting sheet 10A is scattered in various directions in the light-adjusting layer 20. Therefore, the normal type light-adjusting sheet 10A is in an opaque state when no driving voltage is applied. The light-adjusting sheet 10A in the opaque state looks, for example, cloudy white.

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

[0029] The polymer network type light control layer 20 is formed by irradiating ultraviolet rays to a coating film consisting of a mixture of an ultraviolet-polymerizable compound for forming a polymer network 21 and a liquid crystal composition 23. That is, 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 ultraviolet rays are irradiated to the coating film through these laminates, thereby forming a normal type light control sheet 10A having a polymer network type light control layer 20.

[0030] Next, the layer structure of the reverse-type light controlling sheet will be described with reference to FIG. 3 and FIG. 3, the reverse-type light-controlling sheet 10B includes a first alignment layer 51 and a second alignment layer 52 in addition to the light-controlling layer 20, transparent electrode layers 31 and 32, and transparent support layers 41 and 42. The first alignment layer 51 is located between the light-controlling layer 20 and the first transparent electrode layer 31 and is in contact with these layers. The second alignment layer 52 is located between the light-controlling 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 alignment of the liquid crystal molecules 24. The alignment layers 51 and 52 are, for example, vertical alignment films. The vertical alignment films align the liquid crystal molecules 24 so that their long axis directions are along the thickness direction of the light control layer 20. When the alignment layers 51 and 52 are vertical alignment films, the liquid crystal molecules 24 are made of liquid crystal molecules with negative dielectric anisotropy, i.e., liquid crystal molecules whose dielectric constant in the long axis direction is smaller than that in the short axis direction.

[0032] The material of the alignment layers 51 and 52 is, for example, polyimide, polyamide, or polyvinyl alcohol. , organic compounds such as cyanide compounds, inorganic compounds such as silicon oxide and zirconium oxide, silicone, etc. The alignment treatment for forming the alignment layers 51 and 52 is, for example, a rubbing treatment, a polarized light irradiation treatment, or a microfabrication treatment.

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

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

[0035] A reverse-type light-controlling sheet 10B having a polymer network-type light-controlling layer 20 is formed by sandwiching the above-mentioned coating film between a laminate of a first alignment layer 51, a first transparent electrode layer 31, and a first transparent support layer 41, and a laminate of a second alignment 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 structure of the light-adjusting sheet is not limited to the above, as long as the light-adjusting sheet is configured to switch between a transparent state and an opaque state based on a change in the alignment state of the liquid crystal molecules caused by application of a driving voltage. For example, the light-adjusting sheet may include a polarizing layer that controls the polarization of incident light or transmitted light to the light-adjusting layer 20, and the alignment layers 51 and 52 may be horizontal alignment films. Whether the light-adjusting sheet becomes transparent or opaque when a driving voltage is applied can be changed depending on the presence or absence of the alignment layers 51 and 52, the direction in which the alignment regulating force of 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, and the like.

[0037] At least one of the front and back surfaces of the light-controlling sheet is attached to a transparent plate made of glass, resin, or the like. The transparent plate is, for example, a window glass provided in various buildings, a partition installed indoors, or a window glass or windshield provided in a moving body such as a vehicle or an aircraft. The surface of the transparent plate may be flat or curved. The light-controlling sheet of this embodiment uses a liquid crystal composition having a property that allows good switching between a transparent state and an opaque state in a low-temperature environment, and is therefore suitable for use in vehicle-mounted components that are required to be usable in a low-temperature environment. That is, the light-controlling sheet of this embodiment is suitable for application to vehicle window glass.

[0038] [Characteristics of liquid crystal composition] The characteristics of the liquid crystal composition used in the light controlling sheet of this embodiment will be described in detail. The main component of the liquid crystal composition is liquid crystal molecules. The liquid crystal molecules are, for example, one selected from the group consisting of Schiff base type, azo type, azoxy type, biphenyl type, terphenyl type, benzoic acid ester type, tolan type, pyrimidine type, pyridazine type, cyclohexane carboxylate type, phenylcyclohexane type, biphenylcyclohexane type, dicyanobenzene type, naphthalene type, and dioxane type. The liquid crystal composition may contain only a single type of liquid crystal molecule as the 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. The components other than liquid crystal molecules may include, for example, a viscosity reducing agent, a dichroic dye, an antifoaming agent, an antioxidant, a weathering agent such as an ultraviolet absorbing agent or a light stabilizer. In order to obtain good anisotropy of the liquid crystal composition and good optical properties of the light control sheet, such as light transmittance and haze, the mass ratio of all the liquid crystal molecules in the liquid crystal composition is preferably 80% or more with respect to the total mass of the liquid crystal composition.

[0040] The viscosity of the liquid crystal composition changes depending on the temperature, and the lower the temperature, the greater the viscosity. If the viscosity of the liquid crystal composition is too high in a low-temperature environment, the liquid crystal molecules are less likely to move, and the alignment state of the liquid crystal molecules is less likely to change in response to the application of a driving voltage. As a result, the responsiveness of the light transmittance in the light-controlling sheet decreases, that is, it takes time to switch between the transparent state and the opaque state, or the switching is not possible. In the light-controlling layer 20, as described above, the liquid crystal molecules change their orientation within the minute domains partitioned within the transparent polymer layer. Therefore, compared to a structure in which the liquid crystal composition is filled in a wide layered region such as a liquid crystal panel used in a display device, the viscosity of the liquid crystal composition has a large effect on the ease of changing the alignment state of the liquid crystal molecules, and the responsiveness of the light transmittance is likely to be low in a low-temperature environment.

[0041] The viscosity of a liquid crystal composition changes nonlinearly with temperature, increasing rapidly as the temperature decreases. The degree of increase in viscosity from room temperature to low temperatures varies depending on the composition of the liquid crystal composition. The inventors of the present application therefore calculated the degree of change in viscosity of a liquid crystal composition at low and high temperatures based on the viscosity at room temperature (23°C) as a reference, and discovered that by using the calculated results, it is possible to evaluate the responsiveness of the light transmittance of a light-controlling sheet at temperatures other than room temperature.

[0042] That is, if the maximum viscosity Vm, which is the maximum value of the viscosity of the liquid crystal composition in the range of -20°C to 110°C, is 100 times or less the reference viscosity Vb, which is the viscosity of the liquid crystal composition at 23°C, the light controlling sheet can be switched between the transparent state and the opaque state well in the above temperature range. As described 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, 10 mPa·s or more and 500 mPa·s or less. If the reference viscosity Vb is within the above range, the light-control sheet can be quickly switched between the transparent and opaque states at 23°C, and since the maximum viscosity Vm is 100 times or less than the reference viscosity Vb, the light-control sheet can be switched between the transparent and opaque states at a speed similar to that at room temperature even in a low-temperature environment. For example, the switching between the transparent and opaque states is completed within 60 seconds after 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 the liquid crystal composition can be adjusted by the type of liquid crystal molecules contained in the liquid crystal composition, whether or not a viscosity reducing agent is added to the liquid crystal composition, and the amount of the viscosity reducing agent added. The viscosity reducing agent has 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 the maximum viscosity Vm to the reference viscosity Vb can be reduced. As such a viscosity reducing agent, for example, an alkenyl compound represented by the following structural formula (1) can be used. In order to obtain good anisotropy of the liquid crystal composition and optical properties of the light control sheet, the content ratio of the viscosity reducing agent in the liquid crystal composition is preferably 10% or less with respect to the total mass of the liquid crystal composition. [ka] Furthermore, by adding a chiral agent that gives a twist to the liquid crystal molecules to the liquid crystal composition, The viscosity of the composition can also be fine-tuned.

[0045] In addition, the NI point (Nematic-Isotropic transition temperature) of the liquid crystal composition under atmospheric pressure is preferably 100° C. or higher and 145° C. or lower. Since the liquid crystal composition loses anisotropy at temperatures above the NI point, if the NI point is too low, the liquid crystal molecules are less likely to be aligned in a high-temperature environment, making it difficult to switch the light control sheet between a transparent state and an opaque state. If the NI point is 100° C. or higher, the alignment state of the liquid crystal molecules changes smoothly even in a high-temperature environment, making it possible to smoothly switch between a transparent state and an opaque state.

[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 less, the maximum viscosity Vm of the liquid crystal composition can be prevented from increasing. As described above, it is possible to reduce the viscosity of the liquid crystal composition at low temperatures by adding a viscosity reducing agent, but if the proportion of contents other than liquid crystal molecules in the liquid crystal composition increases, there is a concern that the anisotropy of the liquid crystal composition and the optical properties of the light control sheet may decrease. If the NI point is 145° C. or less, the viscosity of the liquid crystal composition at low temperatures can be reduced so that the maximum viscosity Vm can be 100 times or less the reference viscosity Vb without excessively increasing the amount of viscosity reducing agent added.

[0047] Next, the characteristics of the liquid crystal composition that affect the optical characteristics of the light controlling sheet will be described. In the transparent state of the light-adjusting sheet, it is preferable that visual recognition of an object through the light-adjusting sheet is more clearly possible, i.e., it is preferable that the haze is small. On the other hand, in the opaque state of the light-adjusting sheet, it is preferable that visual recognition of an object through the light-adjusting sheet is more difficult, i.e., it is preferable that the haze is large. Therefore, it is preferable that the difference in haze between the transparent state and the opaque state is large. The haze is measured in accordance with JIS K 7136:2000.

[0048] The larger the refractive index difference Δn (Δn=extraordinary refractive index ne-ordinary refractive index no) between the long axis direction and the short axis direction of the liquid crystal molecule, the larger the difference in the refractive index of the liquid crystal molecules for light incident on the light-controlling layer 20 when a driving voltage is applied and when it is not applied, and therefore the larger the difference in light scattering properties. 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, the refractive index difference Δn is preferably 0.17 or more.

[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 more difficult it is for the liquid crystal molecules to move. Therefore, the larger the refractive index difference Δn of the liquid crystal molecules, the greater the viscosity of the liquid crystal composition at low temperatures, making it more difficult for the alignment state to change. In addition, even at room temperature, the alignment is less likely to be aligned when a driving voltage is applied, so the optical characteristics after the alignment state changes tend to be poor. In order to improve the response of the light transmittance in a low-temperature environment and to improve the optical characteristics, it is preferable that the refractive index difference Δn is 0.28 or less.

[0050] On the other hand, 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 too small, the refractive index difference Δn becomes too small, which results in a deterioration of the optical properties of the light control sheet. Therefore, in order to ensure a refractive index difference Δn that provides a good difference in haze between the transparent state and the opaque state, it is preferable that the maximum viscosity Vm is 30 times or more the reference viscosity Vb, and it is more preferable that the maximum viscosity Vm is 35 times or more the reference viscosity Vb.

[0051] When 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 index in the major axis direction of the multiple types of liquid crystal molecules and the average value of the refractive index in the minor axis direction of the multiple types of liquid crystal molecules.

[0052] [Example] The above-mentioned liquid crystal composition and light controlling sheet will be described with reference to specific examples and comparative examples.

[0053] (Liquid crystal composition) Using seven types of liquid crystal materials (MLC-6608, MLC-6609, MLC-6610, MLC-3018, ZLI-2806, ZLI-1131, ZLI-1132) manufactured by Merck, 12 types of liquid crystal compositions of Examples 1 to 9 and Comparative Examples 1 to 3 were prepared. The 12 types of liquid crystal compositions were one type or a mixture of two or more types of the seven types of liquid crystal materials, and had different compositions. In addition, an alkenyl compound represented by the above structural formula (1) was added as a viscosity reducing agent to some of the liquid crystal compositions so that the concentration in the liquid crystal composition was 5 mass %.

[0054] (Light control sheet) A normal type light control sheet having a polymer network type light control layer was prepared using the liquid crystal composition of each Example and Comparative Example. Specifically, an acrylic monomer, which is an ultraviolet-polymerizable compound, was mixed with the liquid crystal composition to prepare a coating liquid, and the coating liquid was applied onto the first transparent electrode layer supported by the first transparent support layer to form a coating film. The first transparent electrode layer supported by the second transparent support layer was layered on the coating film, and the laminate was irradiated with ultraviolet light. As a result, the acrylic monomer in the coating film was polymerized to form a polymer network, and a light control layer in which the liquid crystal composition was held in the polymer network was formed. The refractive index of the polymer network was 1.5. The material of each transparent electrode layer was indium tin oxide, and the material of each transparent support layer was polyethylene terephthalate. The manufacturing conditions, such as the ultraviolet exposure conditions, were set for each Example and Comparative Example so that the haze in the transparent state of the light control sheet was the lowest.

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

[0056] [Light transmittance response] For the light-controlling sheets of each example and each comparative example, the responsiveness of the light transmittance was evaluated by judging whether or not they could be driven at -20°C and 90°C. Specifically, it was judged that the light-controlling sheets could be driven if the switching from the opaque state to the transparent state was completed within 60 seconds after the start of application of the driving voltage to the light-controlling sheets. Completion of the switching from the opaque state to the transparent state means that the change in haze is completed. At 23°C, the light-controlling sheets of each example and each comparative example could be driven.

[0057] [Optical properties] For the light controlling sheets of each of the Examples and Comparative Examples, the haze was measured in both a transparent state and an opaque state 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 liquid crystal compositions of each Example and Comparative Example, including the presence or absence of a viscosity reducing agent, the viscosity 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 the viscosity at -20°C, 0°C, 90°C, and 110°C to the reference viscosity Vb, the NI point, and the refractive index difference Δn of the liquid crystal molecules for the liquid crystal compositions of each Example and Comparative Example. The reference viscosity Vb of the Examples and Comparative Examples to which a viscosity reducing agent is added is the viscosity at 23°C after the viscosity reducing agent is added. Furthermore, Table 2 shows the results of judging whether the light controlling sheets of each Example and Comparative Example can be driven or not, and the results of haze measurements.

[0060] [Table 1]

[0061] [Table 2]

[0062] As shown in Table 2, in the range of -20°C or more and 110°C or less, the viscosity of the liquid crystal composition of each Example and Comparative Example is maximum at -20°C. In Examples 1 to 9, in which the maximum viscosity Vm is 100 times or less than the reference viscosity Vb, the light controlling sheet could be driven at -20°C. On the other hand, in Comparative Examples 1 to 3, in which the maximum viscosity Vm exceeds 100 times the reference viscosity Vb, the light controlling sheet could not be driven at -20°C. Therefore, it was confirmed that if the maximum viscosity Vm is 100 times or less than the reference viscosity Vb, good switching between a transparent state and an opaque state is possible in a low temperature environment.

[0063] Moreover, in Examples 7 and 8, in which the NI point was less than 100° C., the light-controlling sheet could not be driven at 90° C. Therefore, it was confirmed that the NI point needs to be 100° C. or higher in order to enable good switching between the transparent state and the opaque state in a high-temperature environment.

[0064] In addition, in Examples 7 and 9, in which the refractive index difference Δn of the liquid crystal molecules is less than 0.17, the haze in the transparent state is higher than the others, and the haze in the opaque state is lower than the others, so that the difference in haze between the transparent state and the opaque state is small. In detail, in Example 7, the haze in the opaque state is particularly low, so that the difference in haze between the transparent state and the opaque state is small. Therefore, 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, the refractive index in the long axis direction and the short axis direction are present, suggesting that the light scattering in the light control layer in the opaque state is low. On the other hand, in Example 9, the haze in the transparent state is particularly high, so that the difference in haze between the transparent state and the opaque state is small. Therefore, in the region where the refractive index of the liquid crystal molecules in the transparent state is away from the refractive index of the polymer network, the refractive index in the long axis direction and the short axis direction are present, suggesting that light scattering occurs in the light control layer even in the transparent state.

[0065] In Comparative Example 3, in which the refractive index difference Δn exceeds 0.28, the haze in the transparent state is high. This is because the liquid crystal molecules are difficult to move due to their large molecular weight, and as a result, the liquid crystal molecules remain in the transparent state even after switching from the opaque state to the transparent state by application of a driving voltage. It is believed that the molecules are not perfectly aligned and some disorder remains, causing light scattering in the photochromic layer.

[0066] In contrast, in Examples 1 to 6 and 8 and Comparative Examples 1 and 2, in which the refractive index difference Δn is 0.17 or more and 0.28 or less, the haze is good in both the transparent and opaque states, that is, good optical characteristics are obtained.

[0067] Moreover, Examples 7 and 9 suggest that when the maximum viscosity Vm is less than about 30 times the reference viscosity Vb, the refractive index difference Δn becomes too small, and the optical properties deteriorate as described above. As shown by Examples 1 to 6 and 8, when the maximum viscosity Vm is 35 times or more the reference viscosity Vb, the haze becomes good in both the transparent and opaque states, that is, good optical properties are obtained.

[0068] As described above in the embodiments and examples, the liquid crystal composition and the light controlling sheet can provide the following effects. (1) The liquid crystal composition has a maximum viscosity Vm in the range of -20°C to 110°C that is 100 times or less of the reference viscosity Vb at 23°C. This prevents the liquid crystal composition from increasing in viscosity even in a low-temperature environment where the viscosity of the liquid crystal composition increases, to a degree that allows the liquid crystal molecules to change their alignment state favorably upon application of a driving voltage. This allows the liquid crystal composition to be satisfactorily switched between a transparent state and an opaque state in a light control sheet.

[0069] (2) If the maximum viscosity Vm is 30 times or more the reference viscosity Vb, the molecular weight of the liquid crystal molecules is not too small, and the refractive index difference Δn of the liquid crystal molecules is prevented from becoming too small. Therefore, the optical properties such as haze of the light-controlling sheet are obtained well, and a good balance is achieved between suppressing the viscosity of the liquid crystal composition in a low-temperature environment and improving the optical properties. In addition, if the maximum viscosity Vm is 35 times or more the reference viscosity Vb, good haze is easily obtained in both the transparent and opaque states of the light-controlling sheet, that is, good optical properties are easily obtained.

[0070] (3) Since the NI point of the liquid crystal composition under atmospheric pressure is 100°C or higher, the light-adjusting sheet can be smoothly switched between transparent and opaque states in a high-temperature environment. Therefore, the light-adjusting sheet operates well in both low-temperature and high-temperature environments, making it possible to expand the temperature range in which the light-adjusting sheet can be used. In addition, since the NI point is 145°C or lower, it is easy to keep the viscosity of the liquid crystal composition low at low temperatures.

[0071] (4) Since the refractive index difference Δn of the liquid crystal molecules is 0.17 or more, a good difference in haze between the transparent state and the opaque state of the light-controlling sheet can be obtained. In addition, since the above Δn is 0.28 or less, the molecular weight of the liquid crystal molecules is prevented from becoming excessively large, it is possible to suppress the viscosity of the liquid crystal composition in a low-temperature environment and to suppress the liquid crystal molecules from becoming difficult to align when the orientation state of the liquid crystal molecules changes. Therefore, it is possible to improve the response of the light transmittance in a low-temperature environment and the optical properties of the light-controlling sheet.

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

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

[0074] 10A, 10B…Light control sheet 20...Photochromic layer 21…Polymer network 22…Domain 23...Liquid crystal composition 24...Liquid crystal molecule 31,32...Transparent electrode layer 41,42...Transparent support layer 51, 52...Alignment layer

Claims

1. a light control 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; A pair of transparent electrode layers sandwiching the light control layer, a 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 a reference viscosity, the maximum value of the viscosity in the range of −20° C. to 110° C. is 100 times or less of the reference viscosity and is 696 mPa·s to 7275 mPa·s, The liquid crystal composition contains a compound represented by the following formula (1) as the viscosity reducing agent: Dimming sheet. 【Chemistry 1】

2. The maximum viscosity is 30 times or more the reference viscosity. The light controlling sheet according to claim 1 .

3. The maximum viscosity is 35 times or more the reference viscosity. The light controlling sheet according to claim 2 .

4. The maximum viscosity is the viscosity of the liquid crystal composition at −20° C. The light controlling sheet according to any one of claims 1 to 3.

5. The NI point of the liquid crystal composition under atmospheric pressure is in the range of 100° C. to 145° C. The light controlling sheet according to any one of claims 1 to 4.

6. The difference in refractive index between the major axis direction and the minor axis direction of the liquid crystal molecule is 0.17 or more and 0.28 or less. The light controlling sheet according to any one of claims 1 to 5.

7. The liquid crystal composition contains the liquid crystal molecules having a positive dielectric anisotropy. The light controlling sheet according to any one of claims 1 to 6.

8. The liquid crystal composition contains the liquid crystal molecules having negative dielectric anisotropy. The light controlling sheet according to any one of claims 1 to 6.

9. The light control layer is sandwiched between the light control layer and the pair of transparent electrode layers. The light controlling sheet according to claim 8.

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