Filter

Abstract

The present invention addresses the problem of providing a novel filter for use in a band-pass filter or the like. The problem is solved by having three or more groups of liquid crystal layer groups including a first liquid crystal layer in which a liquid crystal compound is twisted and fixed, and a second liquid crystal layer in which the twisting direction of the liquid crystal compound is opposite to that of the first liquid crystal layer, the orientation direction of the liquid crystal compound at the interface between the first liquid crystal layer and the second liquid crystal layer being parallel to each other. The distortion angles of the liquid crystal compounds in the first liquid crystal layer and the second liquid crystal layer are equal.

Description

Technical Field

[0001] The present invention relates to an optical filter. Background Art

[0002] Bandpass filters that transmit light in a specific wavelength range and block light of other wavelengths are used in various optical devices.

[0003] As bandpass filters, there are known polarization interference filters using dielectric multilayer films, filters in which a polarization element and a birefringent crystal are combined, and the like.

[0004] Furthermore, as described in Patent Document 1, a bandpass filter is also known, in which birefringent plates (λ / 2 plates) of equal thickness and in which the angle between the transmission axis of the polarizer and the slow axis is +ρ and birefringent plates of -ρ are alternately stacked between polarizers arranged in a crossed Nicols manner.

[0005] In addition, in patent document 1, as an optical filter (bandpass filter) with a small number of parts, an optical filter is proposed, which is composed of a crystal, the crystal having a structure in which two different polarization regions are periodically arranged, and the main axes of the refractive index ellipsoids cut parallel to the interfaces of the two different polarization regions are different in the two different polarization regions.

[0006] Previous technical literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-101577 Summary of the Invention

[0009] Technical issues to be solved by the invention

[0010] As described above, bandpass filters having various structures are known.

[0011] An object of the present invention is to provide a novel filter that is different from these and can be used for a bandpass filter or the like.

[0012] Means for solving technical problems

[0013] In order to solve the problem, the present invention has the following configuration.

[0014] [1] A filter having three or more liquid crystal layer groups in a thickness direction, the liquid crystal layer groups comprising:

[0015] The first liquid crystal layer is formed by fixing a liquid crystal compound in a twisted orientation in the thickness direction.

[0016] The second liquid crystal layer is formed by fixing a liquid crystal compound in a twisted orientation in the thickness direction, wherein the twist direction of the liquid crystal compound is opposite to the twist direction of the liquid crystal compound in the first liquid crystal layer.

[0017] In the liquid crystal layer group, the alignment direction of the liquid crystal compound on the surface of the first liquid crystal layer on the second liquid crystal layer side is parallel to the alignment direction of the liquid crystal compound on the surface of the second liquid crystal layer on the first liquid crystal layer side.

[0018] The twist angle of the liquid crystal compound in the first liquid crystal layer is equal to the twist angle of the liquid crystal compound in the second liquid crystal layer.

[0019] [2] The filter according to [1], wherein

[0020] A polarizer is provided in a manner such that three or more liquid crystal layer groups are sandwiched in the thickness direction.

[0021] The polarizers sandwiching three or more liquid crystal layer groups in the thickness direction are arranged so that their transmission axes are perpendicular to each other.

[0022] [3] The filter according to [1] or [2], wherein

[0023] In the liquid crystal layer groups arranged on both sides in the thickness direction and the liquid crystal layer group arranged in the center in the thickness direction, the twist angles of the liquid crystal compounds in the first liquid crystal layer and the second liquid crystal layer and the Δnd in the first liquid crystal layer and the second liquid crystal layer are different from each other.

[0024] [4] The filter according to any one of [1] to [3], wherein

[0025] The liquid crystal compound in the first liquid crystal layer includes a rod-like liquid crystal compound and a discotic liquid crystal compound, and the liquid crystal compound in the second liquid crystal layer includes a rod-like liquid crystal compound and a discotic liquid crystal compound.

[0026] [5] The filter according to any one of [1] to [4], wherein

[0027] The first liquid crystal layer and the second liquid crystal layer contain infrared absorbing pigments.

[0028] [6] The filter according to any one of [1] to [5], wherein

[0029] The first liquid crystal layer and the second liquid crystal layer include liquid crystal elastomer.

[0030] [7] The filter according to any one of [1] to [6], wherein

[0031] When the total number of stacked first and second liquid crystal layers is N and the twist angles of the liquid crystal compounds in the first and second liquid crystal layers are ±φ[°], the following equation is satisfied:

[0032] 0.9×(129.05×N -0.961 )≤|φ|≤1.1×(129.05×N -0.961 ).

[0033] [8] The filter according to any one of [2] to [7], wherein

[0034] A phase difference layer is provided between one or both of the polarizers and the three or more liquid crystal layer groups.

[0035] Furthermore, the in-plane slow axis of the phase difference layer is parallel to any absorption axis of the polarizer.

[0036] Effects of the Invention

[0037] According to the present invention, a novel filter that can be used for a bandpass filter or the like is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a diagram schematically showing an example of the filter of the present invention.

[0039] Figure 2 This is a graph for explaining the filter of the present invention.

[0040] Figure 3 This is a graph for explaining the filter of the present invention.

[0041] Figure 4 This is a diagram schematically showing another example of the filter of the present invention.

[0042] Figure 5 Is used to illustrate Figure 4 Diagram of the filter shown. DETAILED DESCRIPTION

[0043] Hereinafter, the liquid crystal diffraction element of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0044] In this specification, the numerical range expressed using "to" means a range including the numerical values described before and after "to" as the lower limit and the upper limit.

[0045] Furthermore, the drawings shown below are all conceptual diagrams for explaining the present invention, and the positional relationship, size, thickness, shape, etc. of each component are different from the actual ones.

[0046] exist Figure 1 , an example of the filter of the present invention is schematically shown.

[0047] Figure 1 The filter 10 shown is a bandpass filter (narrow band filter) that transmits light in a specific wavelength range and blocks light of other wavelengths, and includes a first polarizer 12, a second polarizer 14, and a liquid crystal polarization interference element 16. The liquid crystal polarization interference element 16 is disposed between the first polarizer 12 and the second polarizer 14.

[0048] In the filter 10 shown in the figure, the first polarizer 12 and the second polarizer 14 are provided as a preferred embodiment.

[0049] That is, the filter of the present invention may be constituted only by the liquid crystal polarization interference element 16 in the filter 10 shown in the figure.

[0050] The first polarizer 12 and the second polarizer 14 are polarizers (polarizing plates) that transmit linearly polarized light in a predetermined direction, and are arranged in a crossed Nicol configuration that is perpendicular to the transmission axis.

[0051] The first polarizer 12 and the second polarizer 14 are not limited, and various well-known linear polarizers such as an iodine-based polarizer, a dye-based polarizer using a dichroic dye, a polyene-based polarizer, and a wire grid polarizer can be used.

[0052] In the filter 10 shown in the figure, a liquid crystal polarization interference element 16 is arranged between the first polarizer 12 and the second polarizer 14 .

[0053] In addition, Figure 1 In the embodiment, the first polarizer 12 and the second polarizer 14 are separated from the liquid crystal polarization interference element 16.

[0054] However, the present invention is not limited to this, and the first polarizer 12 and the second polarizer 14 may be in contact with and stacked on the liquid crystal polarization interference element 16. Furthermore, when the first polarizer 12 and the second polarizer 14 are in contact with the liquid crystal polarization interference element 16, they may be bonded together using an adhesive transparent to transmitted light, such as an OCA (Optical Clear Adhesive) or an acrylic adhesive, as needed.

[0055] The liquid crystal polarization interference element 16 is an optical element that functions as a λ / 2 phase difference plate for light in a specific wavelength region (specific wavelength) and does not function as a phase difference layer for other light.

[0056] As described above, the first polarizer 12 and the second polarizer 14 are polarizers arranged in a crossed Nicol system that is perpendicular to the transmission axis.

[0057] Therefore, of the light incident on the filter 10, only linearly polarized light in a predetermined direction passes through the first polarizer 12. Of this linearly polarized light, light of a specific wavelength has its polarization direction rotated 90° by the liquid crystal polarization interference element 16, and then enters and passes through the second polarizer 14, which is arranged in a crossed Nicols arrangement with the first polarizer 12. In contrast, because the liquid crystal polarization interference element 16 does not function as a retardation layer, light other than that in the specific wavelength region enters and is blocked by the first polarizer 12 and the second polarizer 14, which is arranged in a crossed Nicols arrangement.

[0058] Due to this optical action, the filter 10 becomes a bandpass filter that transmits only light in a specific wavelength range and blocks other light.

[0059] The liquid crystal polarization interference element 16 is an element in which an even number of liquid crystal layers are stacked, each of which is formed by fixing a twisted orientation of a liquid crystal compound 18 in the thickness direction. The liquid crystal compound 18 is a rod-shaped liquid crystal compound.

[0060] Specifically, the liquid crystal polarization interference element 16, that is, the filter of the present invention, is an element formed by alternatingly stacking a first liquid crystal layer 20 formed by a liquid crystal compound 18 with a twisted orientation fixed in the thickness direction and a second liquid crystal layer 24 formed by a liquid crystal compound 18 with a twisted orientation fixed in the thickness direction and the twisting direction of the first liquid crystal layer 20 and the liquid crystal compound 18 in the opposite direction.

[0061] The liquid crystal polarization interference element 16 has a structure in which a combination of one first liquid crystal layer 20 and a second liquid crystal layer 24 constitutes one liquid crystal layer group 26 and three or more liquid crystal layer groups 26 are stacked in the thickness direction.

[0062] Therefore, the total number of stacked layers of the first liquid crystal layer 20 and the second liquid crystal layer 24 is an even number.

[0063] In one liquid crystal layer group 26 , the alignment direction of the liquid crystal compound 18 on the surface of the first liquid crystal layer 20 on the second liquid crystal layer 24 side is parallel to the alignment direction of the liquid crystal compound on the surface of the second liquid crystal layer 24 on the first liquid crystal layer 20 side.

[0064] That is, in one liquid crystal layer group 26 , the alignment directions of the liquid crystal compounds 18 are parallel at the interface between the first liquid crystal layer 20 and the second liquid crystal layer 24 .

[0065] In a liquid crystal layer group 26, the orientation direction of the liquid crystal compound 18 on the surface of the first liquid crystal layer 20 on the second liquid crystal layer 24 side and the orientation direction of the liquid crystal compound 18 on the surface of the second liquid crystal layer 24 on the first liquid crystal layer 20 side can be detected by obliquely cutting the liquid crystal polarization interference element 16 and analyzing the orientation direction of the liquid crystal on the surface of its cross section.

[0066] This method is described in detail in "Depth-Dependent Determination of Molecular Orientation for WV-Film" by Yohei Takahashi et al. (FMC8-3, IDW'04, 651-654).

[0067] In one liquid crystal layer group 26 , the twist angle of the liquid crystal compound 18 in the first liquid crystal layer 20 in the thickness direction is equal to the twist angle of the liquid crystal compound 18 in the second liquid crystal layer 24 in the thickness direction.

[0068] As described above, the liquid crystal compound 18 of the first liquid crystal layer 20 and the second liquid crystal layer 24 have opposite twist directions in the thickness direction. Specifically, for example, if the twist angle of the liquid crystal compound 18 in the first liquid crystal layer 20 is "φ [°]", the twist angle of the liquid crystal compound 18 in the first liquid crystal layer 20 becomes "-φ [°]".

[0069] Therefore, in a single liquid crystal layer group 26, the twist of the liquid crystal compound 18 is twisted to a certain angle in the thickness direction in the first liquid crystal layer 20 and then twisted back to its original state in the second liquid crystal layer 24. For example, if the twist angle of the liquid crystal compound 18 in the thickness direction is 30°, the liquid crystal compound 18 is twisted from 0° to 30° in the first liquid crystal layer 20 and then twisted back from 30° to 0° in the second liquid crystal layer 24.

[0070] In this example, regarding the twist angle (twist angle) of the liquid crystal compound, as an example, the direction of the transmission axis of the first polarizer 12 is set to 0°, the clockwise direction is set to positive (+), and the counterclockwise direction is set to negative (-).

[0071] That is, the absolute values of the twist angles of the first liquid crystal layer 20 and the second liquid crystal layer 24 are equal.

[0072] As described above, in the liquid crystal polarization interference element 16, the liquid crystal compound 18 (rod-shaped liquid crystal compound) is twistedly oriented in the thickness direction. In addition, the orientation of the liquid crystal compound 18 at the interface is parallel and the twisting direction of the liquid crystal compound 18 is opposite, and the first liquid crystal layer 20 and the second liquid crystal layer 24 with the same absolute value of the twisting angle are alternately stacked in the thickness direction.

[0073] That is, light passing through the liquid crystal polarization interference element 16 is alternately and repeatedly affected by the slow axis rotating in one direction by a predetermined angle and by the slow axis rotating in the opposite direction by a predetermined angle. For example, when the absolute value of the twist angle of the liquid crystal compound 18 is 30°, light passing through the liquid crystal polarization interference element 16 is alternately and repeatedly affected by the slow axis rotating from 0° to 30° and by the slow axis rotating from 30° to 0°.

[0074] Therefore, in the liquid crystal polarization interference element 16, the Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 is set according to the wavelength region of the transmission filter 10, and the twist angle of the liquid crystal compound in the first liquid crystal layer 20 and the second liquid crystal layer 24 is adjusted according to the total number of stacking layers of the first liquid crystal layer 20 and the second liquid crystal layer 24. This can form a liquid crystal polarization interference element 16 that acts as a λ / 2 phase difference plate for light in a specific wavelength region but does not act as a phase difference plate for light other than this wavelength region, that is, no delay is perceived.

[0075] The number of liquid crystal layer groups 26 in the liquid crystal polarization interference element 16 can be detected by obliquely cutting the liquid crystal polarization interference element 16 and analyzing the orientation of the liquid crystal on the surface of the cross section. This method is described in detail in the aforementioned document by Yohei Takahashi et al.

[0076] Furthermore, changes in the twisting direction of the liquid crystal can be detected based on differences in the chiral reagent using a TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) device, for example, based on differences in composition along the depth direction of the device. Examples of TOF-SIMS devices include the TOF and SIMS5 manufactured by ION-TOF.

[0077] In the Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 constituting the liquid crystal polarization interference element 16, Δn represents the birefringence of the liquid crystal compound 18 constituting the first liquid crystal layer 20 and the second liquid crystal layer 24. Furthermore, d represents the thickness of the first liquid crystal layer 20 and the second liquid crystal layer 24. Δn can also be measured using an AxoScan manufactured by Axometrics, Inc., or the like.

[0078] In the present invention, Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 are equal.

[0079] As described above, the liquid crystal polarization interference element 16 functions as a λ / 2 retardation plate only for light within a specific wavelength range. Accordingly, the Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 is set to half (half) the center wavelength of the wavelength range in which the liquid crystal polarization interference element 16 is assumed to function as a λ / 2 retardation plate, that is, the wavelength of the wavelength assumed to be transmitted through the filter 10.

[0080] For example, assuming that the center wavelength of the wavelength range in which the filter 10 transmits light, at which the liquid crystal polarization interference element 16 functions as a λ / 2 phase difference plate, is 550 nm, the Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 is set to 275 nm.

[0081] Furthermore, the Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 may have an error of approximately ±10% with respect to half the center wavelength of the wavelength range transmitted by the filter 10 .

[0082] On the other hand, regarding the twist angle of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 constituting the liquid crystal polarization interference element 16, the optimal twist angle for the liquid crystal polarization interference element 16 to function as a λ / 2 phase difference plate is set through simulation based on the center wavelength of the wavelength range of the assumed transmission filter 10 and the total stacking number N of the first liquid crystal layer 20 and the second liquid crystal layer 24.

[0083] This simulation can be performed using a normal optical simulation mechanism or LCD Master 1D (manufactured by SHINTECH Co., Ltd., Ver. 9.8.0.0).

[0084] Here, according to the simulation by the present inventors, the twist angle φ of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 is N, which is the total number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24.

[0085] When the number of stacked layers N is 2 (one liquid crystal layer group), the twist angle φ is 63.6°.

[0086] When the number of stacked layers N is 4 (two liquid crystal layer groups), the twist angle φ is 35.5°.

[0087] When the number of stacked layers N is 6 (3 liquid crystal layer groups), the twist angle φ is 23.6°.

[0088] When the number of stacked layers N is 8 (4 liquid crystal layer groups), the twist angle φ is 17.7°.

[0089] When the number of stacked layers N is 10 (5 liquid crystal layer groups), the twist angle φ is 14.1°.

[0090] When the number of stacked layers N is 12 (6 liquid crystal layer groups), the twist angle φ is 11.8°.

[0091] When the number of stacked layers N is 14 (7 liquid crystal layer groups), the twist angle φ is 10.1°.

[0092] When the number of stacked layers N is 16 (8 liquid crystal layer groups), the twist angle φ is 8.8°.

[0093] The above are appropriate values.

[0094] like Figure 2 As shown schematically, if the result (solid line) is fitted with an approximate curve (dashed line), it is well consistent with the following formula,

[0095] φ=129.05×N -0.961 .

[0096] Accordingly, in the present invention, the twist angles ±φ [°] of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 corresponding to the total number N of stacked layers of the first liquid crystal layer 20 and the second liquid crystal layer 24 are preferably set to:

[0097] 0.9×(129.05×N -0.961 )≤|φ|≤1.1×(129.05×N -0.961 ),

[0098] More preferably, it is:

[0099] |φ|=129.05×N -0.961 .

[0100] Furthermore, the absolute values of the twist angles of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 are not necessarily the same, and may have an error of ±10% or less in the absolute value of the twist angle.

[0101] However, it is preferable that the error be small, and it is most preferable that the absolute values of the twist angles of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 match each other.

[0102] The twist angles of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 constituting the liquid crystal polarization interference element 16 can be detected by obliquely cutting the liquid crystal polarization interference element 16 and analyzing the orientation of the liquid crystal on the surface of the cross section. This method is described in detail in the aforementioned document by Yohei Takahashi et al.

[0103] The twist angle of the liquid crystal compound 18 can also be measured using AxoScan (manufactured by Axometrics, Inc.) by using a separation measurement mechanism assuming a model with input parameters.

[0104] The thickness d of the first liquid crystal layer 20 and the second liquid crystal layer 24 is not limited either. Depending on the liquid crystal compound 18 used, the thickness may be appropriately set so that Δnd becomes half the wavelength of the center wavelength of the wavelength range through which the filter 10 transmits.

[0105] The thickness d of the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably 1 to 5 μm, more preferably 1 to 3 μm.

[0106] The first liquid crystal layer 20 and the second liquid crystal layer 24 are generally formed using the same liquid crystal compound 18. Furthermore, the Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 are equal. Therefore, the thickness of the first liquid crystal layer 20 and the second liquid crystal layer 24 are equal.

[0107] The total stacking number N of the first liquid crystal layer 20 and the second liquid crystal layer 24 is not limited as long as the number of liquid crystal layer groups 26 is 3 or more, that is, 6 or more, and is an even number.

[0108] The total number N of stacked layers of the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably 6 to 30 layers, more preferably 6 to 20 layers, and even more preferably 6 to 10 layers.

[0109] In the filter 10 of the present invention, the greater the total number N of stacked first and second liquid crystal layers 20 and 24, that is, the greater the number of liquid crystal layer groups 26, the narrower the wavelength range in which the liquid crystal polarization interference element 16 functions as a λ / 2 phase difference layer.

[0110] Therefore, in the filter 10 of the present invention, the greater the total number N of stacked first and second liquid crystal layers 20, 24, the narrower the half-value width (FWHM) of the wavelength range of the transmitted light. In other words, the greater the total number N of stacked first and second liquid crystal layers 20, 24, the narrower the transmission wavelength range of the filter 10.

[0111] Therefore, the total stacking number N of the first liquid crystal layer 20 and the second liquid crystal layer 24, that is, the number of liquid crystal layer groups 26, is determined according to the width of the transmission wavelength region required by the filter 10. When a broadband is preferred, a smaller number of layers is selected, and when a narrowband is required, a larger number of layers can be appropriately selected.

[0112] Such a liquid crystal polarization interference element 16 may be produced by a known method.

[0113] As one example, the first liquid crystal layer 20 and the second liquid crystal layer 24 are produced by a coating method using a liquid crystal composition for forming the first liquid crystal layer 20 and the second liquid crystal layer 24 .

[0114] First, an alignment film aligned in one direction is formed on an appropriately selected support.

[0115] The alignment film can utilize the following well-known alignment films: a friction-treated film composed of an organic compound such as a polymer, an oblique vapor-deposited film of an inorganic compound, a film having microgrooves, a film formed by accumulating an LB (Langmuir-Blodgett) film of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride and methyl stearate based on the Langmuir-Blodgett method, and a film formed by coating a coating liquid for forming an alignment film containing a photo-alignment material on the surface of a support, drying the coating liquid, and exposing the coating film using a polarizer such as a wire grid polarizer.

[0116] On the other hand, a composition (liquid crystal composition) for forming the first liquid crystal layer 20 and a composition for forming the second liquid crystal layer 24 are prepared, wherein the composition contains a chiral agent having a function of inducing a liquid crystal compound and twisting the liquid crystal compound in the thickness direction.

[0117] The liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 has opposite twist directions in the thickness direction. However, the twist direction of the liquid crystal compound in the thickness direction can be selected by selecting a chiral agent. Furthermore, the twist angle of the liquid crystal compound 18 in the thickness direction can be adjusted by adjusting the amount of chiral agent added.

[0118] The solvent used to prepare the composition is not limited and can be appropriately selected according to the purpose, but is preferably an organic solvent. The organic solvent is not limited and can be appropriately selected according to the purpose, and examples thereof include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These can be used alone or in combination of two or more. Among these, ketones are preferred when considering the burden on the environment.

[0119] The composition for forming the first liquid crystal layer 20 is applied onto the surface of the formed alignment film, the liquid crystal compound 18 is aligned, and then dried. If necessary, the composition is cured by ultraviolet irradiation or the like, thereby forming the first liquid crystal layer 20 .

[0120] Next, a composition for forming the second liquid crystal layer 24 is applied onto the surface of the formed first liquid crystal layer 20 and dried. If necessary, the composition is cured by ultraviolet irradiation or the like to form the second liquid crystal layer 24, thereby forming a first liquid crystal layer group.

[0121] Here, when a liquid crystal layer is formed on the liquid crystal layer by a coating method, the upper liquid crystal layer follows the alignment of the liquid crystal compound on the surface of the lower liquid crystal layer.

[0122] Therefore, at the interface between the first liquid crystal layer 20 and the second liquid crystal layer 24 , the alignment direction of the liquid crystal compound 18 in the first liquid crystal layer 20 and the alignment direction of the liquid crystal compound 18 in the second liquid crystal layer 24 are parallel (aligned).

[0123] Next, a composition for forming the first liquid crystal layer 20 is applied onto the surface of the formed second liquid crystal layer 24 , dried, and if necessary, cured by ultraviolet irradiation or the like, thereby forming the first liquid crystal layer 20 .

[0124] In the liquid crystal polarization interference element 16 constituting the filter 10 of the present invention, the twist angles of the liquid crystal compound 18 in the thickness direction in the first liquid crystal layer 20 and the twist angles of the liquid crystal compound 18 in the thickness direction in the second liquid crystal layer are equal, and the twist directions are opposite. Therefore, if the orientation angle of the liquid crystal compound 18 at the interface between the first liquid crystal layer 20 and the orientation film formed on the surface of the orientation film is set to 0°, the orientation angle of the liquid crystal compound 18 on the upper surface of the second liquid crystal layer 24 also returns to 0°.

[0125] Furthermore, as described above, when a liquid crystal layer is formed on the liquid crystal layer by a coating method, the upper liquid crystal layer follows the alignment of the liquid crystal compound on the surface of the lower liquid crystal layer.

[0126] Therefore, at the interface between the second liquid crystal layer 24 and the first liquid crystal layer 20 , the alignment direction of the liquid crystal compound 18 in the second liquid crystal layer 24 and the alignment direction of the liquid crystal compound 18 in the first liquid crystal layer 20 are parallel at 0°.

[0127] Next, the second liquid crystal layer 24 is similarly formed on the surface of the first liquid crystal layer 20 formed, and then the first liquid crystal layer 20 is similarly formed on the surface of the second liquid crystal layer 24 formed, and then the second liquid crystal layer 24 is similarly formed on the surface of the first liquid crystal layer 20 formed. This step is repeated according to the number of liquid crystal layers to be formed, that is, the number of liquid crystal layer groups to be formed, thereby producing a liquid crystal polarization interference element 16.

[0128] Furthermore, for example, by aligning the orientation direction of the liquid crystal compound 18 in the first liquid crystal layer 20 formed initially with the transmission axis of the first polarizer 12 (angle 0°), and further arranging the second polarizer 14 to be orthogonal to the first polarizer 12 in Nicols, and arranging them so as to sandwich the liquid crystal polarization interference element 16 in the thickness direction (stacking direction), a structure such as Figure 1 The filter 10 is shown.

[0129] The liquid crystal layer composed of a rod-like liquid crystal compound (rod-like liquid crystal layer) and the liquid crystal layer composed of a discotic liquid crystal compound (disc-like liquid crystal layer) have larger and smaller refractive indices (birefringence), respectively.

[0130] Here, assuming that the larger and smaller refractive indices of the rod-shaped liquid crystal layer are denoted by nc1 and nc2, respectively, and the larger and smaller refractive indices of the discotic liquid crystal layer are denoted by nd1 and nd2, respectively, then from the perspective of suppressing unwanted reflected light, it is preferable that the values of nc1 and nd2 are close, and that the values of nc2 and nd2 are close. Specifically, the difference between these values is preferably 0.05 or less. For example, values such as nc1 = 1.71, nc2 = 1.55, nd1 = 1.67, and nd2 = 1.51 are preferable.

[0131] Furthermore, these refractive indices can be measured optically by peeling off the liquid crystal layer. For example, after treating the liquid crystal layer so that the specular reflectance from the back surface is zero, the incident direction of linearly polarized light when measuring the reflectance spectrum using a spectrophotometer (manufactured by JASCO Corporation, UV-Vis-NIR Spectrophotometer V-750) is aligned with the axis of the respective refractive index to be measured, and the angular dependence of the reflectance obtained from the measurement can be fitted with the calculation formula to determine the refractive index.

[0132] In addition, in the liquid crystal polarization interference element 16 of the filter 10 of the present invention, the first liquid crystal layer 20 and the second liquid crystal layer 24 are not limited to directly stacked layers formed by the coating method as described above. That is, the liquid crystal polarization interference element 16 can be an element formed by making a sheet-like first liquid crystal layer 20 and a second liquid crystal layer 24, alternately stacking them, and bonding them with an optical bonding layer transparent to transmitted light, such as OCA, acrylic adhesive, adhesive, and polymer layer. In this case, from the perspective of improving transmittance, the refractive index of the optical bonding layer is preferably close to the refractive index of the liquid crystal. Specifically, the difference in refractive index is preferably 0.3 or less. Moreover, when the refractive index of the optical bonding layer becomes a value between the two birefringence indices possessed by the liquid crystal, the difference in refractive index becomes smaller compared to either of the two refractive indices, and therefore it is preferred.

[0133] However, from the viewpoint of transmittance of transmitted light, it is preferable to directly stack the first liquid crystal layer 20 and the second liquid crystal layer 24 by a coating method without an adhesive layer or the like.

[0134] In the filter 10 (liquid crystal polarization interference element 16 ) of the present invention, the liquid crystal compound 18 (rod-shaped liquid crystal compound) is not limited, and various known liquid crystal compounds can be used.

[0135] Preferred rod-shaped liquid crystal compounds include azomethines, azoxides, cyanobiphenyls, cyanophenyl esters, benzoates, phenyl cyclohexanecarboxylates, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans, and alkenylcyclohexylbenzonitriles. Furthermore, in the present invention, not only the low-molecular-weight liquid crystal molecules described above but also high-molecular-weight liquid crystal molecules can be used.

[0136] The rod-like liquid crystal compound is more preferably fixed in alignment by polymerization.

[0137] Examples of polymerizable rod-shaped liquid crystal compounds include those described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Pat. No. 4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. No. 5,770,107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Application No. 1-272551, Japanese Patent Application No. 6-16616, Japanese Patent Application No. 7-110469, Japanese Patent Application No. 11-80081, and Japanese Patent Application No. 2001-64627. Furthermore, as the rod-like liquid crystal compound, for example, rod-like liquid crystal compounds described in JP-A-11-513019 and JP-A-2007-279688 can also be preferably used.

[0138] As described above, a chiral agent has the function of inducing a twisted orientation of a liquid crystal compound in the thickness direction. The twisting direction and pitch of the helix induced by the chiral agent vary depending on the compound, and thus can be selected according to the intended purpose.

[0139] The chiral agent is not particularly limited, and known compounds, isosorbide, and isomannide derivatives can be used. Examples of known compounds include those described in "Handbook of Liquid Crystal Devices, Chapter 3, Item 4-3, TN (twisted nematic) and STN (super twisted nematic) chiral agents, page 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989." Specifically, isosorbide refers to a chiral agent having an isosorbide structure.

[0140] Furthermore, chiral reagents that reduce helical twisting power (HTP) by undergoing reverse isomerization, dimerization, isomerization and dimerization, etc. upon irradiation with light can also be preferably used.

[0141] Chiral agents generally contain asymmetric carbon atoms, but axial chiral compounds or planar chiral compounds without asymmetric carbon atoms can also be used as chiral agents. Examples of axial chiral compounds or planar chiral compounds include binaphthyl, helicene, p-xylene dimer and their derivatives. Chiral agents can also have polymerizable groups. In the case where both the chiral agent and the liquid crystal compound have polymerizable groups, a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent can be formed by polymerization of the polymerizable chiral agent and the polymerizable liquid crystal compound. In this manner, the polymerizable group possessed by the polymerizable chiral agent is preferably a group of the same type as the polymerizable group possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridine group, more preferably an unsaturated polymerizable group, further preferably an ethylenically unsaturated polymerizable group.

[0142] Furthermore, the chiral agent may also be a liquid crystal compound.

[0143] When the chiral agent has a photoisomerizable group, it is preferably capable of forming a pattern having a desired reflection wavelength corresponding to the emission wavelength by irradiation with a photomask such as activating light after coating and alignment. The photoisomerizable group is preferably an isomerized site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in JP-A-2002-080478, JP-A-2002-080851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292.

[0144] The twist angle of the liquid crystal compound 18 in the thickness direction changes depending on the amount of the chiral agent added.

[0145] Therefore, by selecting a chiral agent and appropriately setting the added amount, the twist direction and twist angle of the liquid crystal compound 18 in the first liquid crystal layer 20 and the second liquid crystal layer 24 can be arbitrarily set.

[0146] In addition to the liquid crystal compound and the chiral agent, a polymerization initiator, a leveling agent, a crosslinking agent, a surfactant, and the like may be added to the composition for forming the first liquid crystal layer 20 and the second liquid crystal layer 24 as needed.

[0147] Figure 1 In the filter 10 shown, all first liquid crystal layers 20 are identical, and all second liquid crystal layers 24 are also identical. Figure 1 In the filter 10 shown, the Δnd of all first liquid crystal layers 20 and the twist angle of the liquid crystal compound 18 are equal, and the Δnd of all second liquid crystal layers 24 and the twist angle of the liquid crystal compound 18 are equal.

[0148] However, the present invention is not limited to this, and the Δnd of the liquid crystal layer and the twist angle of the liquid crystal compound 18 may be distributed in the thickness direction. That is, in the filter of the present invention, if the Δnd is equal in the first and second liquid crystal layers, and the twist directions of the liquid crystal compound 18 are opposite and the twist angles (absolute values of the twist angles) are equal, then different Δnds and twist angles of the liquid crystal compound 18 may exist in the liquid crystal layer groups.

[0149] As an example, a structure is described in which the Δnd of the liquid crystal layer and the twist angle of the liquid crystal compound 18 are different between the liquid crystal layer group at the center in the thickness direction (stacking direction) and the liquid crystal layer groups on both sides in the thickness direction.

[0150] Specifically, the Δnd of the liquid crystal layers of the liquid crystal layer groups on both sides in the thickness direction can be made larger than that of the liquid crystal layer of the central liquid crystal layer group in the thickness direction, and the twist angle of the liquid crystal compound 18 can be made smaller.

[0151] As will be shown later in the examples, as an example, when the filter (liquid crystal polarization interference element) has eight liquid crystal layers, that is, four liquid crystal layer groups, the following is shown:

[0152] In the first liquid crystal layer group, the Δnd of the first liquid crystal layer (first layer) is set to Δnd1, the twist angle of the liquid crystal compound is set to φ1, the Δnd of the second liquid crystal layer (second layer) is set to Δnd1, the twist angle of the liquid crystal compound is set to -φ1,

[0153] In the second liquid crystal layer group, the Δnd of the first liquid crystal layer (the third layer) is set to Δnd2 which is smaller than Δnd1, and the twist angle of the liquid crystal compound is set to φ2 which is larger than φ1. The Δnd of the second liquid crystal layer (the fourth layer) is set to Δnd2, and the twist angle of the liquid crystal compound is set to -φ2.

[0154] In the third liquid crystal layer group, the Δnd of the first liquid crystal layer (the fifth layer) is set to Δnd2, the twist angle of the liquid crystal compound is set to φ2, the Δnd of the second liquid crystal layer (the sixth layer) is set to Δnd2, the twist angle of the liquid crystal compound is set to -φ2,

[0155] In the fourth group of liquid crystal layers, the Δnd of the first liquid crystal layer (the seventh layer) is set to Δnd1, the twist angle of the liquid crystal compound is set to φ1, the Δnd of the second liquid crystal layer (the eighth layer) is set to Δnd1, and the twist angle of the liquid crystal compound is set to -φ1.

[0156] In a bandpass filter, such as Figure 3 As schematically shown, transmission wavelength regions called side lobes are generated at positions with wavelengths shorter and longer than the target transmission wavelength region, as indicated by arrows S in the figure.

[0157] In contrast, as described above, the side lobes can be reduced by making the Δnd of the liquid crystal layers of the liquid crystal layer groups on both sides in the thickness direction larger than that of the liquid crystal layer of the central liquid crystal layer group in the thickness direction and reducing the twist angle of the liquid crystal compound 18 .

[0158] Furthermore, as an example, Δnd of the liquid crystal layer can be adjusted by changing the thickness of the liquid crystal layer, but it can also be adjusted by changing the liquid crystal compound used.

[0159] Furthermore, the twist angle of the liquid crystal compound can be adjusted by changing the type and / or amount of the chiral agent added.

[0160] In this structure in which the Δnd of the liquid crystal layers of the liquid crystal layer groups on both sides in the thickness direction is greater than that of the liquid crystal layers of the central liquid crystal layer group in the thickness direction and the twisting angle of the liquid crystal compound 18 is reduced, there is no restriction on the number of layers of the central liquid crystal layer that makes the Δnd of the liquid crystal layer greater than that of the two sides and the twisting angle of the liquid crystal compound 18 is reduced, that is, the way of dividing the liquid crystal layer groups on both sides and the center, and it can be appropriately set according to the number of liquid crystal layers (liquid crystal layer groups) possessed by the filter.

[0161] Furthermore, the Δnd of the liquid crystal layer and the twist angle of the liquid crystal compound 18 of the liquid crystal layer groups on both sides in the thickness direction, as well as the Δnd of the liquid crystal layer and the twist angle of the liquid crystal compound 18 of the liquid crystal layer group in the center in the thickness direction can also be simulated to set the liquid crystal polarization interference element to function as a λ / 2 phase difference plate and to have the optimal Δnd and twist angle that can reduce the side lobes.

[0162] Furthermore, it is preferable to control the change in the twist angle of the liquid crystal compound 18 from both sides toward the center in the stacking direction (thickness direction) and the distribution of Δnd in the thickness direction of the liquid crystal layer of the liquid crystal layer group as gradually and finely as possible.

[0163] exist Figure 1 In the filter 10 shown, the liquid crystal compound 18 in each liquid crystal layer is a rod-shaped liquid crystal compound, and the liquid crystal layer is composed only of the rod-shaped liquid crystal compound, but the present invention is not limited to this.

[0164] That is, in the filter of the present invention, the liquid crystal layer is as follows Figure 4 Like the first liquid crystal layer 32 and the second liquid crystal layer 34 of the filter 30 shown in the figure, a discotic liquid crystal compound may be included in addition to the liquid crystal compound 18 .

[0165] In the following description, the liquid crystal compound 18 is also referred to as the rod-shaped liquid crystal compound 18 in order to clearly distinguish it from the discotic liquid crystal compound 40. Figure 4 In the filter 30 shown, the same components are denoted by the same reference numerals, and the following description will focus on the different components.

[0166] exist Figure 4 In the filter 30 shown, the first liquid crystal layer 32 and the second liquid crystal layer 34 are also liquid crystal layers formed by fixing the rod-shaped liquid crystal compound 18 and the discotic liquid crystal compound 40 in twisted alignment in the thickness direction.

[0167] Furthermore, in the filter 30, the twist directions of the liquid crystal compounds in the first liquid crystal layer 32 and the second liquid crystal layer 34 are opposite, and the twist angles of the liquid crystal compounds are the same. That is, the total twist angle of the rod-shaped liquid crystal compound 18 and the discotic liquid crystal compound 40 in the first liquid crystal layer 32 and the second liquid crystal layer 34 is in the relationship of "φ" and "-φ" similar to the above example.

[0168] Furthermore, in the filter 30 , the alignment directions of the liquid crystal compounds at the interface between the first liquid crystal layer 32 and the second liquid crystal layer 34 are also parallel.

[0169] exist Figure 4 In the filter 30 shown, the first liquid crystal layer 32 has, in the thickness direction from bottom to top in the figure, firstly, the rod-shaped liquid crystal compound 18 with twisted alignment in the thickness direction, and then the discotic liquid crystal compound 40 with twisted alignment in the thickness direction.

[0170] In contrast, the second liquid crystal layer 34 thereon has, in the thickness direction from the bottom toward the top in the figure, a disc-shaped liquid crystal compound 40 with a twisted orientation in the thickness direction, and furthermore, a rod-shaped liquid crystal compound 18 with a twisted orientation in the thickness direction. The twisted orientation directions of the liquid crystal compounds in the first liquid crystal layer 32 and the second liquid crystal layer 34 are opposite.

[0171] The filter 30 also includes a liquid crystal polarization interference element 46 in which the first liquid crystal layer 32 and the second liquid crystal layer 34 are alternately stacked, and the liquid crystal polarization interference element 46 includes three or more liquid crystal layer groups consisting of the first liquid crystal layer 32 and the second liquid crystal layer 34.

[0172] exist Figure 4 In the illustrated example, in the liquid crystal layer group 36, the first liquid crystal layer 32 comprises a rod-like liquid crystal compound / disc-like liquid crystal compound, and the second liquid crystal layer 34 comprises a disc-like liquid crystal compound / rod-like liquid crystal compound, as shown in the figure, from bottom to top in the thickness direction. However, the present invention is not limited to this. For example, in the filter of the present invention, the first liquid crystal layer may comprise a rod-like liquid crystal compound / disc-like liquid crystal compound, and the second liquid crystal layer may comprise a rod-like liquid crystal compound / disc-like liquid crystal compound, as shown in the figure, from bottom to top in the thickness direction.

[0173] Furthermore, the number, order, and thickness of the regions composed of the rod-like liquid crystal compound 18 and the regions composed of the discotic liquid crystal compound 40 can be appropriately changed while maintaining the sum of Δnd and the twist angle of the liquid crystal compound in each liquid crystal layer constant.

[0174] like Figure 5 As schematically shown, in a bandpass filter, when light is incident from an oblique direction, a wavelength shift occurs in which the transmission wavelength range shifts to the shorter wavelength side.

[0175] In contrast to color change, by having the first liquid crystal layer 32 and the second liquid crystal layer 34 have regions composed of rod-shaped liquid crystal compounds 18 and regions composed of disc-shaped liquid crystal compounds 40, the phase difference (Rth) in the thickness direction of the first liquid crystal layer 32 and the second liquid crystal layer 34 can be reduced, thereby suppressing the wavelength shift (color change) when light is incident from an oblique direction.

[0176] When the first liquid crystal layer 32 and the second liquid crystal layer 34 are composed of regions composed of the rod-shaped liquid crystal compound 18 and regions composed of the discotic liquid crystal compound 40 , the thickness ratio of the regions composed of the rod-shaped liquid crystal compound 18 to the regions composed of the discotic liquid crystal compound 40 is not limited.

[0177] Here, in the case where the first liquid crystal layer 32 and the second liquid crystal layer 34 are composed of regions composed of rod-shaped liquid crystal compounds 18 and regions composed of disc-shaped liquid crystal compounds 40, it is preferred to divide the Δnd of the liquid crystal layer into half each in the region composed of rod-shaped liquid crystal compounds 18 and the region composed of disc-shaped liquid crystal compounds 40 according to the Δn of the liquid crystal compounds used.

[0178] Furthermore, from the viewpoint of reducing interface reflection, the rod-like liquid crystal compound 18 and the discotic liquid crystal compound 40 preferably have the same Δn value, but compounds having different Δn values may also be used.

[0179] In addition, the liquid crystal polarization interference element 46 composed of a liquid crystal layer having regions composed of rod-like liquid crystal compounds 18 and regions composed of disc-like liquid crystal compounds 40 can also be formed by a coating method using the composition for forming the regions composed of rod-like liquid crystal compounds 18 in the first liquid crystal layer 32, the composition for forming the regions composed of disc-like liquid crystal compounds 40 in the first liquid crystal layer 32, the composition for forming the regions composed of disc-like liquid crystal compounds 40 in the second liquid crystal layer 34, and the composition for forming the regions composed of rod-like liquid crystal compounds 18 in the second liquid crystal layer 34, in the same manner as described above.

[0180] In the case where a region composed of disc-shaped liquid crystal compounds 40 is formed on a region composed of rod-shaped liquid crystal compounds 18, and in the case where a region composed of rod-shaped liquid crystal compounds 18 is formed on a region composed of disc-shaped liquid crystal compounds 40, as described above, the liquid crystal compounds in the upper region follow the orientation direction (longitudinal direction) of the liquid crystal compounds in the lower region.

[0181] Therefore, in such a liquid crystal layer having regions composed of rod-shaped liquid crystal compounds 18 and regions composed of disc-shaped liquid crystal compounds 40, in one liquid crystal layer, the liquid crystal compounds are also continuously twisted in the thickness direction, and the orientation direction of the liquid crystal compounds at the interface between the first liquid crystal layer 32 and the second liquid crystal layer 34 is parallel.

[0182] Furthermore, as described above, the present invention can be applied not only to a liquid crystal layer (region) directly laminated by a coating method but also to a liquid crystal layer in which sheet-like liquid crystal layers are laminated and bonded using OCA or the like.

[0183] In the present invention, when the first liquid crystal layer 32 and the second liquid crystal layer 34 have regions composed of the discotic liquid crystal compound 40 , the discotic liquid crystal compound used is not limited, and various known discotic liquid crystal compounds can be used.

[0184] As the discotic liquid crystal compound, for example, the discotic liquid crystal compounds described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used.

[0185] In addition, when a discotic liquid crystal compound is used in the liquid crystal layer, Figure 4 As shown, the disc-shaped liquid crystal compound 40 stands upright in the thickness direction, and the optical axis derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, that is, a so-called fast axis.

[0186] and, Figure 4 The first liquid crystal layer 32 and the second liquid crystal layer 34 shown each have one region composed of the rod-like liquid crystal compound 18 and one region composed of the discotic liquid crystal compound 40 , but the present invention is not limited thereto.

[0187] That is, in the present invention, when the first liquid crystal layer and the second liquid crystal layer have regions composed of a rod-like liquid crystal compound and regions composed of a disc-like liquid crystal compound, one liquid crystal layer may have a plurality of regions composed of a rod-like liquid crystal compound and / or a plurality of regions composed of a disc-like liquid crystal compound.

[0188] In this case, it is preferable to further subdivide the regions composed of rod-shaped liquid crystal compounds and the regions composed of disc-shaped liquid crystal compounds in a single liquid crystal layer to increase the number of layers. This can reduce the difference between the front (normal) retardation and the retardation at polar angles over a wider range of azimuthal angles.

[0189] The twist angle and twist direction of the liquid crystal compounds in the first liquid crystal layer 32 and the second liquid crystal layer 34 constituting the liquid crystal polarization interference element 46 can be detected by obliquely cutting the liquid crystal polarization interference element 46 and analyzing the orientation of the liquid crystal on the surface of the cross section. This method is described in detail in the aforementioned document by Yohei Takahashi et al.

[0190] In the bandpass filter of the present invention, the transmission axes of the crossed Nicols polarizers sandwiching the liquid crystal polarization interference element 46 are preferably set at an appropriate angle to preferably obtain desired bandpass characteristics. As a preferred example, the angle of the transmission axis can be adjusted to reduce the size of the side lobes generated at wavelengths on both sides of the main bandpass wavelength (long-wavelength side and short-wavelength side) and to equalize the size of the side lobes on the long-wavelength side and the short-wavelength side.

[0191] Furthermore, in the bandpass filter of the present invention, a phase difference layer may be provided between the liquid crystal polarization interference element 46 and one or both sides of the crossed Nicols polarizers provided to sandwich the liquid crystal polarization interference element 46 .

[0192] This retardation layer maintains the orthogonal relationship of polarization directions based on the linear polarizers arranged in a crossed Nicols arrangement not only in the front view, but also in the off-axis tilted direction of the polarizer. This ensures the same excellent bandpass characteristics as in the front view, even in tilted directions. By aligning the in-plane slow axis of the retardation layer with any absorption axis in the crossed Nicols polarizer set, polarization compensation can be achieved, maintaining the orthogonal relationship of polarization directions in tilted directions without affecting the front view.

[0193] Examples of retardation layers include a positive C plate based on vertical alignment of rod-like liquid crystals, a positive A plate based on horizontal alignment of rod-like liquid crystals, a negative C plate based on discotic liquid crystals, a negative A plate based on discotic liquid crystals, and combinations of these retardation layers, such as a combination of a positive C plate based on vertical alignment of rod-like liquid crystals and a positive A plate based on horizontal alignment of rod-like liquid crystals. Furthermore, a biaxial refractive index body, B plate (Nz coefficient of 0.1 to 0.9), can also be used as the retardation layer.

[0194] In the filter of the present invention, the first liquid crystal layer and the second liquid crystal layer may contain an infrared absorbing dye.

[0195] By including infrared-absorbing pigments in the first and second liquid crystal layers, the wavelength dispersion of the liquid crystal in the liquid crystal layers can be made stronger and positive. Consequently, the wavelength range of light in which the liquid crystal polarization interference element functions as a λ / 2 wave plate can be narrowed. Specifically, by adding infrared-absorbing pigments to the first and second liquid crystal layers, the wavelength dispersion of the liquid crystal in the liquid crystal layers can be made stronger and positive, resulting in a bandpass filter with a narrower transmission wavelength range.

[0196] As the infrared absorbing dye, various infrared absorbing dyes that can reduce the difference in refractive index between the x-direction and the y-direction by being aligned in the same direction as the liquid crystal compound can be used.

[0197] Infrared absorbing pigments are not particularly limited as long as they absorb infrared light. Preferably, the infrared absorbing pigment is a dichroic pigment. Infrared light, for example, is light with a wavelength of 700 to 900 nm. Furthermore, a dichroic pigment is a pigment whose absorbance along the long axis of the molecule differs from that along the short axis.

[0198] As infrared absorbing dyes, diketopyrrolopyrrole dyes, diimmonium dyes, phthalocyanine dyes, naphthalocyanine dyes, azo dyes, polymethine dyes, anthraquinone dyes, pyrylium dyes, squarylium dyes, triphenylmethane dyes, cyanine dyes, and ammonium dyes can be used.

[0199] Furthermore, as the infrared absorbing dye, metal complex dyes and boron complex dyes can also be used.

[0200] The infrared absorbing pigment is described in detail in International Publication No. 2019 / 044859.

[0201] The amount of infrared absorbing dye added to the first liquid crystal layer and the second liquid crystal layer is not limited and may be appropriately set according to the width of the transmission wavelength range required for the bandpass filter.

[0202] In the filter of the present invention, the first liquid crystal layer and the second liquid crystal layer may include a liquid crystal elastomer.

[0203] The first liquid crystal layer and the second liquid crystal layer including the liquid crystal elastomer may be formed using the liquid crystal elastomer, or may be formed of a general liquid crystal compound that is not an elastomer and include the liquid crystal elastomer.

[0204] By including liquid crystal elastomer in the first and second liquid crystal layers, the first and second liquid crystal layers can be made elastic, and the thickness of the liquid crystal layer can be changed by stretching or shrinking the filter in the plane direction.

[0205] By varying the thickness of the liquid crystal layer, the Δnd of the liquid crystal layer can be changed. Consequently, in a bandpass filter, the wavelength range of light passing through the filter can be altered. Specifically, by incorporating liquid crystal elastomers into the first and second liquid crystal layers, the wavelength range can be varied by stretching and contracting the liquid crystal layer, i.e., the filter, enabling active wavelength control in the bandpass filter.

[0206] The liquid crystal elastomer is not limited, and various known liquid crystal elastomers can be used.

[0207] As a liquid crystal elastomer, for example, one prepared from a liquid crystal monomer, a chiral agent, a crosslinking agent, and a plasticizer as described in Japanese Patent Application Laid-Open No. 2020-131638 can be used. This imparts mechanical properties and rubber elasticity to the liquid crystal elastomer, enabling deformation in response to the external force required for active wavelength control.

[0208] In addition, when the first liquid crystal layer and the second liquid crystal layer are formed by a conventional liquid crystal compound that is not an elastomer and a liquid crystal elastomer is added to impart elasticity, the amount of liquid crystal elastomer added is not limited and can be appropriately set according to the required elasticity, that is, the control range of the transmission wavelength region.

[0209] The filter of the present invention can be used at any wavelength. That is, the filter of the present invention can be used for any electromagnetic wave, such as ultraviolet light, visible light, infrared light, terahertz waves, and millimeter waves.

[0210] As mentioned above, the filter of the present invention has been described in detail. However, the present invention is not limited to the above-mentioned examples, and various improvements and changes can be made without departing from the scope of the present invention.

[0211] Example

[0212] The following examples are given to further specifically illustrate the characteristics of the present invention. The materials, reagents, usage amounts, amounts, ratios, processing contents and processing steps shown in the following examples can be appropriately changed without departing from the main purpose of the present invention. Therefore, the scope of the present invention should not be interpreted restrictively by the specific examples shown below.

[0213] [Preparation of composition]

[0214] As liquid crystal compositions for forming a liquid crystal layer in which a liquid crystal compound is twistedly aligned in the thickness direction, the following compositions C-1, C-2, D-1, and D-2 were prepared.

[0215] In each composition, "C" indicates that the main component of the liquid crystal compound is a rod-shaped liquid crystal compound, and "D" indicates that the main component of the liquid crystal compound is a disc-shaped liquid crystal compound. Furthermore, in each composition, "1" indicates that the chiral agent induces a right-handed twist in the liquid crystal compound, and "2" indicates that the chiral agent induces a left-handed twist in the liquid crystal compound.

[0216] Therefore, composition C-1 is a liquid crystal composition containing a rod-shaped liquid crystal compound as a main component and forming a liquid crystal layer in which the twist direction of the liquid crystal compound in the thickness direction is clockwise twisted.

[0217] Composition C-2 is a liquid crystal composition containing a rod-shaped liquid crystal compound as a main component and forming a liquid crystal layer in which the twist direction of the liquid crystal compound in the thickness direction is left-twisted.

[0218] Composition D-1 is a liquid crystal composition containing a discotic liquid crystal compound as a main component and forming a liquid crystal layer in which the twist direction of the liquid crystal compound in the thickness direction is right-handed.

[0219] Composition D-2 is a liquid crystal composition containing a discotic liquid crystal compound as a main component, and forming a liquid crystal layer in which the twist direction of the liquid crystal compound in the thickness direction is a left-twisted liquid crystal layer.

[0220] Composition C-1

[0221]

[0222] Composition C-2

[0223]

[0224] Composition D-1

[0225]

[0226] Composition D-2

[0227]

[0228] Rod-like liquid crystal compound L-1

[0229] [Chemical Formula 1]

[0230]

[0231] Discotic liquid crystal compound L-2

[0232] [Chemical Formula 2]

[0233]

[0234] Discotic liquid crystal compound L-3

[0235] [Chemical Formula 3]

[0236]

[0237] Leveling agent T-1

[0238] [Chemical Formula 4]

[0239]

[0240] Chiral reagent Ch-A

[0241] [Chemical Formula 5]

[0242]

[0243] Chiral reagent Ch-B

[0244] [Chemical Formula 6]

[0245]

[0246] Chiral reagent Ch-2

[0247] [Chemical Formula 7]

[0248]

[0249] Chiral reagent Ch-3

[0250] [Chemical Formula 8]

[0251]

[0252] [Example 1]

[0253] (Formation of Orientation Film)

[0254] A glass substrate was prepared as a support. The following alignment film-forming coating liquid was applied to the support by spin coating. The support coated with the alignment film-forming coating liquid was dried on a hot plate at 60° C. for 60 seconds to form an alignment film P-1.

[0255] Coating liquid for forming an alignment film

[0256]

[0257] Materials for photo-orientation

[0258] [Chemical Formula 9]

[0259]

[0260] (Exposure of Alignment Film)

[0261] Next, using an ultraviolet exposure device, the alignment film P-1 was irradiated with linearly polarized ultraviolet light using a wire grid polarizer (ProFlux PPL02 manufactured by MOXTEK, Inc.) set so that the transmission axis angle was φ1 (=0°). The illuminance of the ultraviolet light was 4.5 mW / cm 2 The cumulative exposure dose is 300mJ / cm 2 .

[0262] The angle of the absorption axis refers to the angle relative to the longitudinal direction of the support, with the clockwise direction being positive.

[0263] The first liquid crystal layer was formed by applying composition C-1 on the alignment film P-1. Specifically, composition C-1 was first applied on the alignment film P-1, heated, and then cured with ultraviolet light to form a liquid crystal fixing layer.

[0264] More specifically, regarding the liquid crystal fixing layer, the composition C-1 was applied onto the alignment film P-1 to obtain a coating film, which was then heated to 80° C. on a hot plate and then subjected to a high pressure mercury lamp at 300 mJ / cm 2 in a nitrogen atmosphere at 80° C. 2 The coating film was irradiated with ultraviolet rays having a wavelength of 365 nm to fix the alignment of the liquid crystal compound, thereby forming a first liquid crystal layer.

[0265] The thickness of the first liquid crystal layer is 1.72 μm.

[0266] Next, composition C-2 was applied similarly to the formed first liquid crystal layer, heated, and then ultraviolet-cured to form a second liquid crystal layer. The thickness of the second liquid crystal layer was 1.72 μm.

[0267] The first liquid crystal layer and the second liquid crystal layer were formed alternately to form a liquid crystal polarization interference element having 8 liquid crystal layers (4 liquid crystal layer groups) as shown in Table 1 below (reference Figure 1 ).

[0268] [Table 1]

[0269] N d[um] Δn Δnd[nm] Twist angle φ[°] Composition 1 1.72 0.16 275 17.7 C1 2 1.72 0.16 275 -17.7 C2 3 1.72 0.16 275 17.7 C1 4 1.72 0.16 275 -17.7 C2 5 1.72 0.16 275 17.7 C1 6 1.72 0.16 275 -17.7 C2 7 1.72 0.16 275 17.7 C1 8 1.72 0.16 275 -17.7 C2

[0270] In addition, Δn and the twist angle φ of the liquid crystal compound were measured using AxoScan (manufactured by Axometrics, Inc.).

[0271] The twist angle φ of the liquid crystal compound is an angle relative to the direction of the transmission axis of the wire grid polarizer used for exposure of the alignment film, with the clockwise direction being positive.

[0272] The same also applies to the following embodiments regarding the above aspects.

[0273] The alignment film was peeled off from the liquid crystal polarization interference element thus produced, and a linear polarizer was arranged on one side of the stacking direction of the liquid crystal polarization interference element so that the direction of the linear polarized light irradiated on the alignment film was aligned with the transmission axis, and a linear polarizer was arranged on the other side of the stacking direction so as to form crossed Nicols, thereby producing the following: Figure 1 As the linear polarizer, a structure in which transparent protective films were laminated to both the front and back surfaces of a polyvinyl alcohol film in which iodine was adsorbed and oriented was used.

[0274] The characteristics of the fabricated bandpass filter were measured using a spectroradiometer SR-3 manufactured by TOPCON TECHNOHOUSE CORPORATION.

[0275] As a result, the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0276] [Example 2]

[0277] Composition C-3 was prepared by changing the chiral reagent Ch-A in composition C-1 from 0.058 parts by mass to 0.039 parts by mass.

[0278] Composition C-4 was prepared by changing the chiral reagent Ch-B in composition C-2 from 0.099 parts by mass to 0.067 parts by mass.

[0279] Composition C-5 was prepared by changing the chiral reagent Ch-A in composition C-1 from 0.058 parts by mass to 0.076 parts by mass.

[0280] Furthermore, the chiral reagent Ch-B in composition C-2 was changed from 0.099 parts by mass to 0.129 parts by mass to prepare composition C-6.

[0281] Composition C-3 was used to form the first layer (first liquid crystal layer) and the seventh layer (first liquid crystal layer).

[0282] Composition C-4 was used to form the second layer (second liquid crystal layer) and the eighth layer (second liquid crystal layer).

[0283] Composition C-5 was used to form the third layer (first liquid crystal layer) and the fifth layer (first liquid crystal layer).

[0284] Composition C-6 was used to form the fourth layer (second liquid crystal layer) and the sixth layer (second liquid crystal layer).

[0285] A liquid crystal polarization interference element having eight liquid crystal layers (four liquid crystal layer groups) as shown in Table 2 below was formed in the same manner as in Example 1. The film thickness d of the first, second, seventh, and eighth liquid crystal layers was set to 1.82 μm, and the film thickness d of the third to sixth liquid crystal layers was set to 1.67 μm.

[0286] [Table 2]

[0287] N d[um] Δn Δnd[nm] Twist angle φ[°] Composition 1 1.82 0.16 291 12.6 C3 2 1.82 0.16 291 -12.6 C4 3 1.67 0.16 267 22.4 C5 4 1.67 0.16 267 -22.4 C6 5 1.67 0.16 267 22.4 C5 6 1.67 0.16 267 -22.4 C6 7 1.82 0.16 291 12.6 C3 8 1.82 0.16 291 -12.6 C4

[0288] Using this liquid crystal polarization interference element, a bandpass filter was produced in the same manner as in Example 1, and its characteristics were measured in the same manner as in Example 1.

[0289] As a result, the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0290] Furthermore, the side lobes of the manufactured band-pass filter and the band-pass filter of Example 1 were measured using a spectroradiometer SR-3 manufactured by TOPCONTECHNOHOUSE CORPORATION.

[0291] As a result, the side lobe of the band-pass filter of Example 1 was 10%, and the side lobe of the band-pass filter of Example 2 was 3% or less.

[0292] As described above, by making the Δnd of the liquid crystal layers of the liquid crystal layer groups on both sides in the thickness direction larger than the Δnd of the liquid crystal layer of the central liquid crystal layer group in the thickness direction and reducing the twist angle of the liquid crystal compound 18, the side lobes of the bandpass filter can be reduced.

[0293] The size of the side lobe is the ratio of the transmittance of the side lobe to the transmittance of the central wavelength.

[0294] [Example 3]

[0295] As in Example 1, composition C-1 was used to form a region composed of a rod-shaped liquid crystal compound with a thickness of 0.86 μm. On top of the region, composition D-1 was used to form a region composed of a disc-shaped liquid crystal compound with a thickness of 0.86 μm, thereby forming a first liquid crystal layer.

[0296] On the first liquid crystal layer, composition D-2 is used to form a region composed of a disc-shaped liquid crystal compound with a thickness of 0.86 μm, and on the region, composition C-2 is used to form a region composed of a rod-shaped liquid crystal compound with a thickness of 0.86 μm, thereby forming a second liquid crystal layer, thereby preparing a liquid crystal layer group.

[0297] By performing the formation of the liquid crystal layer group four times, a liquid crystal polarization interference element having eight liquid crystal layers (four liquid crystal layer groups) as shown in Table 3 below was formed (reference Figure 4 ).

[0298] [Table 3]

[0299]

[0300] Using this liquid crystal polarization interference element, a Figure 4 The bandpass filter shown was prepared and the characteristics were measured in the same manner as in Example 1.

[0301] As a result, the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0302] Furthermore, the wavelength shift (absolute value) of the fabricated bandpass filter and the bandpass filter of Example 1 was measured using a spectroradiometer SR-3 manufactured by TOPCON TECHNOHOUSE CORPORATION when light was incident at a polar angle of 60° relative to light incident at a polar angle of 90°. Furthermore, light incident at a polar angle of 60° was measured from two directions, azimuth angles of 0° and 90°, and the average value was used as the measured value.

[0303] As a result, in the bandpass filter of Example 1, the wavelength shift of the central wavelength of transmission was 90 nm, whereas in the bandpass filter of Example 3, the wavelength shift of the central wavelength of transmission was less than 5 nm.

[0304] As described above, since the first liquid crystal layer and the second liquid crystal layer have regions composed of rod-like liquid crystal compounds and regions composed of discotic liquid crystal compounds, wavelength shift when light is incident at an oblique angle can be reduced.

[0305] [Example 10]

[0306] Composition C-11 was prepared by changing the chiral reagent Ch-A in composition C-1 from 0.058 parts by mass to 0.038 parts by mass.

[0307] Composition C-12 was prepared by changing the chiral reagent Ch-B in composition C-2 from 0.099 parts by mass to 0.066 parts by mass.

[0308] Composition D-11 was prepared by changing the amount of chiral reagent Ch-2 in composition D-1 from 0.033 parts by mass to 0.022 parts by mass.

[0309] Composition D-12 was prepared by changing the amount of chiral reagent Ch-3 in composition D-2 from 0.033 parts by mass to 0.022 parts by mass.

[0310] In the same manner as in Example 3, a liquid crystal polarization interference element having the liquid crystal layer group shown in the following table was formed.

[0311] In this example, the number of layers was changed from 8 to 12, and the twist angle was changed compared to Example 3. Furthermore, the film thickness d of each liquid crystal layer was 0.86 μm.

[0312] [Table 4]

[0313]

[0314] Using this liquid crystal polarization interference element, a Figure 4 The bandpass filter shown was prepared and its characteristics were measured in the same manner as in Example 1. As a result, the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 80 nm.

[0315] Furthermore, the wavelength shift was measured in the same manner as in Example 3. As a result, the wavelength shift was less than 5 nm.

[0316] [Example 11]

[0317] In the same manner as in Example 3, a liquid crystal polarization interference element having a liquid crystal layer group shown in the following table was formed using a rod-like liquid crystal compound and a discotic liquid crystal compound.

[0318] The film thickness d of each liquid crystal layer is 1.72 μm.

[0319] [Table 5]

[0320] N d[um] Δn Δnd[nm] Twist angle φ[°] Composition 1 1.72 0.16 275 17.7 C1 2 1.72 0.16 275 -17.7 D2 3 1.72 0.16 275 17.7 C1 4 1.72 0.16 275 -17.7 D2 5 1.72 0.16 275 17.7 C1 6 1.72 0.16 275 -17.7 D2 7 1.72 0.16 275 17.7 C1 8 1.72 0.16 275 -17.7 D2

[0321] Using this liquid crystal polarization interference element, a bandpass filter was fabricated in the same manner as in Example 1, and its characteristics were measured in the same manner as in Example 1. The results showed that the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0322] Furthermore, the wavelength shift was measured in the same manner as in Example 3. As a result, the wavelength shift was less than 10 nm.

[0323] [Example 12]

[0324] In the same manner as in Example 3, a liquid crystal polarization interference element having a liquid crystal layer group shown in the following table was formed using a rod-like liquid crystal compound and a discotic liquid crystal compound.

[0325] In this example, the order of the rod-shaped liquid crystal compound layer and the discotic liquid crystal compound layer was different from that in Example 3. Furthermore, the film thickness d of each liquid crystal layer was 0.86 μm.

[0326] [Table 6]

[0327]

[0328] Using this liquid crystal polarization interference element, a Figure 4 The bandpass filter shown was prepared and its characteristics were measured in the same manner as in Example 1. As a result, the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0329] Furthermore, the wavelength shift was measured in the same manner as in Example 3. As a result, the wavelength shift was less than 4 nm.

[0330] [Example 13]

[0331] In the same manner as in Example 3, a liquid crystal polarization interference element having a liquid crystal layer group shown in the following table was formed using a rod-like liquid crystal compound and a discotic liquid crystal compound.

[0332] In this example, the order and number of the rod-shaped liquid crystal compound layer and the discotic liquid crystal compound layer were different from those in Example 3. The film thickness d of each liquid crystal layer was 0.43 μm.

[0333] [Table 7]

[0334]

[0335] Using this liquid crystal polarization interference element, a bandpass filter was fabricated in the same manner as in Example 1, and its characteristics were measured in the same manner as in Example 1. The results showed that the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0336] Furthermore, the wavelength shift was measured in the same manner as in Example 3. As a result, the wavelength shift was less than 3 nm.

[0337] [Example 21]

[0338] A liquid crystal polarization interference element similar to that of Example 12 was formed, except that the liquid crystal layers were bonded together using the optical bonding layer described below after each liquid crystal layer was formed, instead of the method of forming the liquid crystal layers by continuously coating and aligning the liquid crystal layers of the rod-shaped liquid crystal compound and the disc-shaped liquid crystal compound in Example 12. At this time, bonding was performed so that the slow axes of the interfaces of the liquid crystal layers on the bonding surfaces were aligned parallel to each other.

[0339] As the optical bonding layer, an adhesive layer of SK Dyne 2057 manufactured by Soken Chemical & Engineering Co., Ltd. was used.

[0340] Using this liquid crystal polarization interference element, a Figure 4 The bandpass filter shown was prepared and its characteristics were measured in the same manner as in Example 1. As a result, the maximum transmittance was 95%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0341] Furthermore, the wavelength shift was measured in the same manner as in Example 3. As a result, the wavelength shift was less than 4 nm.

[0342] [Example 31]

[0343] In Example 12, Figure 4 In the illustrated bandpass filter, a retardation layer is disposed between the first polarizer 12 of the linear polarizer and the liquid crystal polarization interference element 16. This retardation layer maintains the orthogonal relationship of polarization directions based on the linear polarizers arranged in a crossed Nicols arrangement not only in the front direction but also in the oblique direction.

[0344] Specifically, as a retardation layer, a positive C plate (thickness direction retardation Rth of -90 nm) based on vertical alignment of rod-like liquid crystal compounds and a positive A plate (in-plane retardation Re of 140 nm) based on horizontal alignment of rod-like liquid crystal compounds were sequentially arranged and bonded adjacent to the first polarizer 12. At this time, the in-plane slow axis of the positive A plate was set parallel to the absorption axis of the first polarizer 12.

[0345] In this way, a bandpass filter was produced.

[0346] The characteristics of the bandpass filter were measured in the same manner as in Example 1. As a result, the maximum transmittance was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 120 nm.

[0347] Furthermore, the wavelength shift was measured in the same manner as in Example 3. As a result, the wavelength shift was less than 3 nm.

[0348] [Example 4]

[0349] Through simulation, a bandpass filter was produced in the same manner as in Example 1 using a liquid crystal polarization interference element in which an infrared absorbing dye was added to the first liquid crystal layer and the second liquid crystal layer.

[0350] The infrared absorbing dye is required to have dichroic absorption of near infrared light and to be aligned in the same direction as the liquid crystal compound as a guest dye in the liquid crystal compound serving as a host.

[0351] As a result, the Δn(450) / Δn(650) of the produced liquid crystal layer was 1.4, the maximum transmittance of the bandpass filter was 99%, the central wavelength of the transmitted light was 550 nm, and the half-value width of the transmitted light was 60 nm.

[0352] As described above, the bandpass filter of Example 1 has a maximum transmittance of 93%, a central wavelength of transmitted light of 550 nm, and a half-value width of transmitted light of 120 nm. By adding infrared-absorbing dyes to the first and second liquid crystal layers, the half-value width of transmitted light is narrowed, resulting in a bandpass filter with a narrower wavelength range for transmitted light.

[0353] [Example 5]

[0354] Through simulation, a bandpass filter was produced in the same manner as in Example 1, using a liquid crystal elastomer as the rod-like liquid crystal compound forming the first liquid crystal layer and the second liquid crystal layer.

[0355] The conditions for the liquid crystal elastomer were as follows: a liquid crystal elastomer prepared using a liquid crystal monomer, a chiral agent, a cross-linking agent, and a plasticizer as described in Japanese Patent Application Laid-Open No. 2020-131638 was used.

[0356] The maximum transmittance of the bandpass filter is 99%, the central wavelength of the transmitted light is 550 nm, and the half-value width of the transmitted light is 60 nm.

[0357] Furthermore, the liquid crystal polarization interference element of the manufactured bandpass filter can be stretched by 20%, and the center wavelength of the transmitted light can be controlled to 50 nm by stretching.

[0358] It can be seen from the above results that the effect of the present invention is obvious.

[0359] Industrial applicability

[0360] The filter of the present invention can be preferably used as a bandpass filter or the like in various optical devices.

[0361] Explanation of symbols

[0362] 10, 30 - filter, 12 - first polarizer, 14 - second polarizer, 16, 46 - liquid crystal polarization interference element, 18 - liquid crystal compound (rod-shaped liquid crystal compound), 20, 32 - first liquid crystal layer, 24, 34 - second liquid crystal layer, 26, 36 - liquid crystal layer group.

Claims

1. A filter comprising three or more liquid crystal layer groups in a thickness direction, the liquid crystal layer groups comprising: The first liquid crystal layer is formed by fixing a liquid crystal compound in a twisted orientation in the thickness direction. The second liquid crystal layer is formed by fixing a liquid crystal compound in a twisted orientation in the thickness direction, wherein the twist direction of the liquid crystal compound is opposite to the twist direction of the liquid crystal compound in the first liquid crystal layer. In the liquid crystal layer group, the alignment direction of the liquid crystal compound on the surface of the first liquid crystal layer on the second liquid crystal layer side is parallel to the alignment direction of the liquid crystal compound on the surface of the second liquid crystal layer on the first liquid crystal layer side, The twist angle of the liquid crystal compound in the first liquid crystal layer is equal to the twist angle of the liquid crystal compound in the second liquid crystal layer.

2. The filter according to claim 1, wherein A polarizer is provided so as to sandwich the three or more liquid crystal layer groups in the thickness direction. The polarizers sandwiching the three or more liquid crystal layer groups in the thickness direction are arranged so that their transmission axes are orthogonal to each other.

3. The filter according to claim 1 or 2, wherein In the liquid crystal layer group arranged on both sides in the thickness direction and the liquid crystal layer group arranged in the center in the thickness direction, the twist angles of the liquid crystal compounds in the first liquid crystal layer and the second liquid crystal layer, and Δnd in the first liquid crystal layer and the second liquid crystal layer are different from each other.

4. The filter according to claim 1 or 2, wherein The liquid crystal compound in the first liquid crystal layer includes a rod-shaped liquid crystal compound and a disc-shaped liquid crystal compound, and the liquid crystal compound in the second liquid crystal layer includes a rod-shaped liquid crystal compound and a disc-shaped liquid crystal compound.

5. The filter according to claim 1 or 2, wherein The first liquid crystal layer and the second liquid crystal layer include infrared absorbing pigments.

6. The filter according to claim 1 or 2, wherein: The first liquid crystal layer and the second liquid crystal layer include liquid crystal elastomer.

7. The filter according to claim 1 or 2, wherein: When the total number of stacked layers of the first liquid crystal layer and the second liquid crystal layer is N and the twist angles of the liquid crystal compounds in the first liquid crystal layer and the second liquid crystal layer are ±φ[°], the following formula is satisfied: 0.9×(129.05×N -0.961 )≤|φ|≤1.1×(129.05×N -0.961 )。 8. The filter according to claim 2, wherein A phase difference layer is provided between one or both of the polarizers and the three or more liquid crystal layer groups. Furthermore, the in-plane slow axis of the phase difference layer is parallel to any one absorption axis of the polarizer.

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