Cholesteric liquid crystal film and its manufacturing method

Abstract

Provided is a cholesteric liquid crystal film that contains cholesteric liquid crystals and has, on the upper side according to microscopic observation, a striped pattern in which dark regions and light regions are aligned side-by-side in alternation in a linear configuration. Also provided is a method for producing the cholesteric liquid crystal film.

Description

[Technical Field]

[0001] The present disclosure relates to cholesteric liquid crystal films and methods for making the same. [Background technology]

[0002] It is known that a striped pattern of dark and light areas can be observed in a cholesteric liquid crystal film when observed under a microscope.

[0003] For example, FIG. 6 of WO 2018 / 043678 shows a photograph of a cross section of a cholesteric liquid crystal film taken by SEM, in which a striped pattern of dark and light areas can be seen.

[0004] For example, FIG. 5 of JP-A-2005-37735 shows a photograph of the cross-sectional structure of a cholesteric liquid crystal polarized selective reflection layer taken with a transmission electron microscope, in which a striped pattern consisting of dark and light areas can be seen. Summary of the Invention [Problem to be solved by the invention]

[0005] The dark and light striped pattern in the cholesteric liquid crystal film, which can be seen under a microscope, indicates the alignment state of the cholesteric liquid crystal. When observed from above with a microscope, a striped pattern of dark and light areas is observed, indicating that the refractive index changes periodically, which is expected to broaden the range of uses for cholesteric liquid crystal films.

[0006] Therefore, the present disclosure has been made in consideration of the above circumstances. An object of one embodiment of the present disclosure is to provide a cholesteric liquid crystal film whose refractive index changes periodically and a method for manufacturing the same. [Means for solving the problem]

[0007] Specific means for solving the problems include the following aspects. <1> comprising a cholesteric liquid crystal; and When observed under a microscope, the top surface of the cholesteric liquid crystal film has a striped pattern of alternating dark and light areas in straight lines. <2> When observed under a microscope, the upper surface has bonding points where the dark areas are bonded to each other, and the number of such bonding points is 10 or less per 50 μm square area. <1> The cholesteric liquid crystal film according to claim 1. <3> The distance between adjacent dark areas is 0.01 μm to 50 μm. <1> or <2> The cholesteric liquid crystal film according to claim 1. <4> When observed under a microscope, a cross section in the thickness direction has a striped pattern in which dark and light areas are alternately arranged, and the dark areas are inclined with respect to the main surface. <1> ~ <3> 10. The cholesteric liquid crystal film according to any one of claims 1 to 9. <5> The inclination angle of the dark portion with respect to the principal surface is 20° to 90°. <4> The cholesteric liquid crystal film according to claim 1. <6> a first step of applying a coating liquid containing a solvent, a liquid crystal compound, and a chiral agent onto a substrate to form a coating film; A second step of applying shear force to the formed coating surface with a blade; and The shear rate in the second step is 1000 s -1 This completes the method for producing a cholesteric liquid crystal film. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, a cholesteric liquid crystal film having a periodically varying refractive index and a method for manufacturing the same are provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an example of a microscope photograph of the top surface of a cholesteric liquid crystal film according to the present disclosure (specifically, the cholesteric liquid crystal film of Example 1). [Figure 2(A)] FIG. 1 is a schematic diagram showing an example of a striped pattern observed from above with a microscope. [Figure 2(B)] FIG. 1 is a schematic diagram showing an example of a striped pattern observed from above with a microscope. [Figure 2(C)]FIG. 1 is a schematic diagram showing an example of a striped pattern observed from above with a microscope. [Figure 2(D)] FIG. 1 is a schematic diagram showing an example of a striped pattern observed from above with a microscope. [Figure 3] 1 is a schematic diagram showing an example of a stripe pattern (i.e., a cross-sectional stripe pattern) observed by microscopic observation of a cross section of a cholesteric liquid crystal film in the thickness direction. [Figure 4] 1 is a schematic diagram showing an example of the molecular arrangement of rod-shaped liquid crystal compounds in a cross section of a cholesteric liquid crystal film. [Figure 5] 1A to 1C are schematic diagrams illustrating an example of a method for producing a cholesteric liquid crystal film according to the present disclosure. [Figure 6] 1 is a photograph of the cholesteric liquid crystal film of Comparative Example 1 observed from above with a polarizing microscope. [Figure 7] 10 is a photograph of the cholesteric liquid crystal film of Comparative Example 2 observed from above with a polarizing microscope. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

[0011] When describing embodiments of the present disclosure with reference to the drawings, descriptions of overlapping components and reference numerals in the drawings may be omitted. Components indicated by the same reference numerals in the drawings are the same components. The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

[0012] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0013] In the present disclosure, when a plurality of substances corresponding to each component are present in the coating liquid, the amount of each component in the coating liquid means the total amount of the plurality of substances present in the coating liquid, unless otherwise specified.

[0014] In the present disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0015] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0016] In the present disclosure, the "upper surface" means the surface of the cholesteric liquid crystal film that is observed under a microscope, and corresponds to the main surface of the cholesteric liquid crystal film. In the present disclosure, the term "main surface" refers to the surface having the major area among the surfaces of an object, and when referring to a "pair of main surfaces," this refers to the front and back surfaces of a film-like object such as a cholesteric liquid crystal film. From the viewpoint of manufacturing, the "pair of main surfaces" are preferably arranged parallel to each other. Here, "parallel to each other" means that the angle between one main surface and the other main surface is less than ±5 degrees.

[0017] In the present disclosure, the term "molecular axis" refers to an axis passing through the center of a molecular structure along the longitudinal direction of the molecular structure, except that the term "molecular axis" used in relation to a discotic liquid crystal compound refers to an axis perpendicular to the discotic plane of the discotic liquid crystal compound.

[0018] In the present disclosure, the term "solid content" refers to all components of the object excluding the solvent. In the present disclosure, the term "mass of solid content" refers to the mass of the object minus the mass of the solvent.

[0019] <Cholesteric liquid crystal film> The cholesteric liquid crystal film according to the present disclosure is a cholesteric liquid crystal film that contains cholesteric liquid crystals and has, when observed under a microscope, a striped pattern of alternating dark and light areas arranged in straight lines on the top surface. That is, when the upper surface of the cholesteric liquid crystal film according to the present disclosure is observed under a microscope, a striped pattern of alternating dark and light areas is seen on the upper surface. In the present disclosure, the "striped pattern in which dark and light areas are alternately arranged in a straight line" is also referred to as a "straight striped pattern."

[0020] When observed under a microscope, the cholesteric liquid crystal film according to the present disclosure has a striped pattern of alternating light and dark areas arranged in straight lines on the top surface, as described above. It is presumed that the presence of such a striped pattern causes the refractive index to change periodically in accordance with the intervals between the dark and bright areas. As a result, it is believed that the cholesteric liquid crystal film according to the present disclosure can be applied to diffraction gratings, polarizing elements, anti-reflection films, etc. by utilizing the function of periodically changing refractive index.

[0021] Although the aforementioned International Publication No. 2018 / 043678 and Japanese Patent Application Laid-Open No. 2005-37735 show striped patterns of alternating dark and light areas in the liquid crystal film, these are only seen when observing a cross section of the liquid crystal film in the thickness direction (i.e., not when observing the liquid crystal film from above with a microscope), and do not have the configuration of the cholesteric liquid crystal film according to the present disclosure.

[0022] [Cholesteric liquid crystal] The cholesteric liquid crystal film according to the present disclosure includes cholesteric liquid crystals. Cholesteric liquid crystals have a layered structure consisting of layers made up of molecules of liquid crystal compounds. Within each layer, the molecules of each liquid crystal compound are aligned in a fixed direction (i.e., their molecular axes are aligned in a fixed direction), and the alignment direction of the molecules in each layer shifts in a spiral shape as they move in the stacking direction, forming a helical structure. The axis of this helical structure is called the helical axis of the cholesteric liquid crystal.

[0023] [Microscope observation from above] As described above, linear stripes are observed on the top surface of the cholesteric liquid crystal film according to the present disclosure under a microscope. For microscopic observation, an optical microscope, a scanning electron microscope (also called SEM), or a polarizing microscope is used. For microscopic observation, an optical microscope, a scanning electron microscope (SEM), or a polarizing microscope may be used depending on the pitch of the stripe pattern (i.e., the distance between dark areas or the distance between light areas). Furthermore, when a scanning electron microscope (SEM) is used for microscopic observation, the cut surface obtained by cutting a pair of main surfaces (i.e., the front and back surfaces) of the cholesteric liquid crystal film with a microtome is used as the top surface, and this cut surface is observed. Note that, if the cutting thickness is 10% or less (preferably 5% or less) of the film thickness of the cholesteric liquid crystal film, observation of the cut surface may be considered as observation of the alignment state of the liquid crystal compound on the top surface. Note that the cutting thickness is preferably 0.5 μm or less.

[0024] Microscopic observation from above is performed on both of the pair of main surfaces (i.e., the front and back surfaces) of the cholesteric liquid crystal film, and it is sufficient if linear stripe patterns are visible on at least one surface, but it is preferable that linear stripe patterns are visible on both surfaces. Here, the area of the upper surface to be observed is, for example, at least 10,000 μm 2 Let's say. In the present disclosure, a "linear stripe pattern" is defined as a pattern in which at least 10 linear dark and light areas are alternately arranged in the above-described microscope observation.

[0025] In the present disclosure, the term "straight line" refers not only to a geometrically strict straight line but also to a line that can be considered to be roughly straight, and may include a line that is slightly curved or a line that includes a curved portion in part. More specifically, the term "straight line" means that the direction in which the dark and light areas extend may have some fluctuation, with the direction being used as a reference line. The specific value of the amplitude is preferably 5 μm or less, and more preferably 2 μm or less.

[0026] Here, the amplitude is determined by the following method. This will be explained using a dark area as an example. First, in a microscope observation from above, two points were taken at the center of one dark area in the width direction, spaced 50 μm apart in the longitudinal direction, and the line connecting these two points was designated as the "reference line." The distance between the reference line and the center of the dark area in the width direction that was furthest away from the reference line within the same dark area was measured, and this was designated as the amplitude. The method for determining the amplitude in the bright area is the same as above.

[0027] (Straight stripes) The linear stripe pattern in the cholesteric liquid crystal film according to the present disclosure will be described with reference to FIG. Here, FIG. 1 is an example of a microscope photograph of the cholesteric liquid crystal film according to the present disclosure, taken from the top surface. As shown in FIG. 1, the cholesteric liquid crystal film according to the present disclosure has a striped pattern in which dark and light areas are alternately arranged in straight lines.

[0028] The dark and bright areas observed under a microscope appear because the direction of the molecular axis of the liquid crystal compound that forms the helical structure changes relative to the observation surface (i.e., the upper surface). When observing a cholesteric liquid crystal film containing rod-shaped liquid crystal compounds with a polarizing microscope, areas where the molecular axes of the rod-shaped liquid crystal compounds are oriented perpendicular (or nearly perpendicular; the same applies below) to the observation surface appear relatively bright. On the other hand, when observing a cholesteric liquid crystal film containing rod-shaped liquid crystal compounds with a polarizing microscope, areas in which the molecular axes of the rod-shaped liquid crystal compounds are parallel (or nearly parallel; the same applies below) to the observation surface appear relatively dark. The two regions described above are arranged alternately in a straight line, resulting in a striped pattern of light and dark regions arranged alternately in a straight line.

[0029] In the linear stripe pattern, the distance between adjacent dark areas is not particularly limited and may be determined depending on the application, etc. For example, it is preferably 0.01 μm to 50 μm, more preferably 0.05 μm to 10 μm, and even more preferably 0.1 μm to 5 μm. It should be noted that as the helical pitch of the cholesteric liquid crystal increases, the distance between adjacent dark areas tends to increase, whereas as the helical pitch decreases, the distance between adjacent dark areas tends to decrease. By providing the distance between adjacent dark portions as described above, the film is suitable for use as a diffraction grating, for example.

[0030] The distance between adjacent dark areas is determined by the following method. When observed under a microscope from above, the shortest distance between five pairs of adjacent dark areas is measured. More specifically, six adjacent dark areas are first selected, and five pairs of adjacent dark areas are extracted from these six dark areas. Then, the shortest distance between adjacent dark areas is measured by measuring the shortest distance between the center of one dark area in the width direction and the center of the other dark area in the width direction within the pair. This measurement is performed for five pairs, and the arithmetic mean value of the five pairs of measurements is taken as the distance between the dark areas.

[0031] (Connection point) In the present disclosure, when observed under a microscope from above, linear stripes are seen over most of the area, but junctions where dark areas join together may also be seen. The connection points will be described with reference to FIGS. 2(A) to 2(D). Here, FIGS. 2(A) to 2(D) are schematic diagrams showing examples of striped patterns observed from above with a microscope. As shown in FIGS. 2(A) to 2(D), there are joining points 30 in the striped pattern where nearby dark portions 10 join together. In FIG. 2(A), there is one connection point 30 where the dark portions 10 are connected to each other. Similarly, there are two connection points 30 in FIG. 2(B), three connection points 30 in FIG. 2(C), and four connection points 30 in FIG. 2(D). In the striped pattern, the dark portions 10 and the light portions 20 are arranged alternately, and therefore, at the connection points 30 where the dark portions 10 are connected to each other, the light portions 20 may also be connected to each other.

[0032] The bonding points are points that disrupt the linear stripe pattern, so it is preferable to have fewer bonding points. Specifically, the number of bonding points is preferably 10 or less, more preferably 5 or less, and even more preferably 3 or less per 50 μm square area. The lower limit of the number of bonding points is most preferably 0 per 50 μm square area, but may be 1 or more from the viewpoint of reducing the amplitude of the dark (or light) areas and increasing the linearity of the dark (or light) areas.

[0033] The number of bonding points is determined by the following method. When observed from above with a microscope, the number of binding points present within a 50 μm square is counted at five different positions. The number of bonding points is determined as the arithmetic mean value of the numbers of bonding points obtained at the five locations.

[0034] [Microscopic observation of cross section in thickness direction] The cholesteric liquid crystal film according to the present disclosure has a striped pattern (hereinafter also referred to as a cross-sectional striped pattern) in which dark and light areas are alternately arranged in a cross section in the thickness direction when observed under a microscope. The cross-sectional stripe pattern will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing an example of a stripe pattern (i.e., a cross-sectional stripe pattern) observed by microscopic observation of a cross section of a cholesteric liquid crystal film in the thickness direction. As shown in FIG. 3, the cholesteric liquid crystal film 1 has a striped pattern in which dark areas 10 and light areas 20 are alternately arranged. The cross-sectional stripe pattern, like the stripe pattern (i.e., the dark and light areas) observed under a microscope from above, appears because the orientation of the molecular axis of the liquid crystal compound that forms a helical structure changes relative to the cross section observed under a microscope.

[0035] For microscopic observation of a cross section in the thickness direction, a scanning electron microscope (i.e., SEM) or a polarizing microscope is used. For microscopic observation of a cross section in the thickness direction, a scanning electron microscope (SEM) or a polarizing microscope may be used depending on the pitch of the stripe pattern (i.e., the distance between dark areas or the distance between light areas). To obtain a cross section in the thickness direction, the cholesteric liquid crystal film may be cut using, for example, a microtome. The cross section in the thickness direction can be observed by rotating the cut surface in 10° increments at 18 positions (i.e., 180°). It is sufficient if the striped pattern and folded structure can be seen at least at one of the 18 positions. Here, the area of the cross section to be observed is, for example, at least 1000 μm 2 Let's say. In the present disclosure, a "cross-sectional stripe pattern" is defined as a pattern in which at least 10 dark and light areas are alternately arranged when the cross section in the thickness direction is observed under a microscope.

[0036] The relationship between the molecular axis of the liquid crystal compound and the cross-sectional stripe pattern will be explained in more detail below. When dark and light areas are observed in a cross section in the thickness direction under a microscope, it is believed that the molecules of the liquid crystal compound in the cholesteric liquid crystal film are arranged, for example, as shown in Fig. 4. Here, Fig. 4 is a schematic diagram showing an example of the molecular arrangement of a rod-like liquid crystal compound in a cross section of a cholesteric liquid crystal film. The cholesteric liquid crystal film 1 shown in Fig. 4 has a pair of principal surfaces (i.e., principal surfaces Fa and Fb) and contains rod-shaped liquid crystal compounds 40, which are represented by ellipses. The rod-shaped liquid crystal compounds 40 are in the form of cholesteric liquid crystals and are aligned in a helical shape along a helical axis HA. That is, since the rod-shaped liquid crystal compounds 40 in the cholesteric liquid crystal film 1 are arranged in a helical shape, the orientation of the molecular axis 40A relative to the cross section observed by the microscope changes along the helical axis. In Fig. 4, the state in which the molecular axis 40A is perpendicular to the cross section observed by the microscope is shown by an ellipse with a short major axis representing the rod-shaped liquid crystal compounds 40, and the state in which the molecular axis 40A is parallel to the cross section observed by the microscope is shown by an ellipse with a long major axis representing the rod-shaped liquid crystal compounds 40.

[0037] 4, the molecules of the rod-shaped liquid crystal compound 40 are aligned, and therefore, a region in which the molecular axis 40A of the rod-shaped liquid crystal compound 40 is parallel to the cross section observed under a microscope (i.e., a region in which the major axis of the ellipse representing the rod-shaped liquid crystal compound 40 is long) is observed as a dark region. For the same reason, a region in which the molecular axis 40A of the rod-shaped liquid crystal compound 40 is perpendicular to the cross section observed under a microscope (i.e., a region in which the ellipse representing the rod-shaped liquid crystal compound 40 is short) is observed as a bright region. Therefore, when the molecules of the rod-like liquid crystal compound 40 are aligned as shown in FIG. 4, a striped cross-sectional pattern as shown in FIG. 3 can be seen when observed under a microscope.

[0038] In the cholesteric liquid crystal film 1 shown in FIG. 4, the helical axis HA is perpendicular to the molecular axis 40A of the rod-like liquid crystal compound 40 and is tilted with respect to each of the principal surfaces Fa and Fb of the cholesteric liquid crystal film 1. By tilting the helical axis HA in this way, the dark portions in the cross-sectional stripe pattern will be tilted with respect to the main surface, as will be described later. The inclination angle of the helical axis HA with respect to the principal planes Fa and Fb is perpendicular to the inclination angle of the dark portions in the cross-sectional stripe pattern with respect to the principal planes. The above has explained the molecular arrangement of liquid crystal compounds in a cholesteric liquid crystal film when bright and dark areas are observed in microscopic observation of a cross section in the thickness direction. The reason why bright and dark areas are observed in microscopic observation from above is the same.

[0039] (Preferred embodiment of cross-sectional stripe pattern) The dark portions in the cross-sectional stripe pattern are preferably inclined with respect to the main surface. That is, the dark portions in the cross-sectional stripe pattern are preferably inclined with respect to the main surface (front or back) of the cholesteric liquid crystal film. Specifically, referring to Fig. 3, the dark portions 10 in the cross-sectional stripe pattern are preferably inclined with respect to the main surfaces Fa and Fb. The inclination of the dark portions makes it easier to obtain a linear stripe pattern on the top surface when observed under a microscope. In the present disclosure, the aspect that "the dark portion is inclined with respect to the main surface" means that the dark portion and the main surface are not parallel to each other as seen by microscopic observation of a cross section in the thickness direction. More specifically, the inclination angle of the dark portions in the cross-sectional stripe pattern relative to the main surface is preferably 20° to 90°, more preferably 30° to 90°, and further preferably 40° to 90°.

[0040] The inclination angle of the dark portion of the cross-sectional stripe pattern relative to the principal surface is determined by the following method. In observing the cross section in the thickness direction with a microscope, the angle θ (specifically, the angle θ shown in Figure 3) between the main surface and a line passing through the center of the width direction at both ends of the longitudinal direction of one dark portion is measured. Except when the angle at the intersection is 90°, the smaller of the angles at the intersection (i.e., the acute angle) is taken as the inclination angle. This measurement is performed for 10 dark portions, and the arithmetic mean value of the measured values for the 10 dark portions is taken as the inclination angle of the dark portion with respect to the main surface.

[0041] In the cross-sectional stripe pattern, the distance between adjacent dark areas is preferably 0.01 μm to 50 μm, more preferably 0.05 μm to 10 μm, and even more preferably 0.1 μm to 5 μm.

[0042] The distance between adjacent dark areas in the cross-sectional stripe pattern is determined in the same manner as the "distance between adjacent dark areas" in the linear stripe pattern.

[0043] [Components contained in cholesteric liquid crystal film] The components contained in the cholesteric liquid crystal film according to the present disclosure will be described below. The cholesteric liquid crystal film according to the present disclosure includes a liquid crystal compound that forms a cholesteric liquid crystal. Furthermore, the cholesteric liquid crystal film according to the present disclosure may contain other components (for example, a chiral agent, a solvent, an alignment regulator, a polymerization initiator, a leveling agent, an alignment aid, a sensitizer, etc.) as needed.

[0044] (liquid crystal compound) The liquid crystal compound contained in the cholesteric liquid crystal film according to the present disclosure is not particularly limited, and for example, known liquid crystal compounds that form cholesteric liquid crystals can be used as the liquid crystal compound.

[0045] The liquid crystal compound may have a polymerizable group. The liquid crystal compound may have one type of polymerizable group alone, or two or more types of polymerizable groups. When the liquid crystal compound has a polymerizable group, the liquid crystal compound can be polymerized. Polymerizing the liquid crystal compound can improve the stability of the cholesteric liquid crystal.

[0046] Examples of the polymerizable group include a group having an ethylenically unsaturated double bond, a cyclic ether group, and a nitrogen-containing heterocyclic group capable of undergoing a ring-opening reaction.

[0047] Examples of the group having an ethylenically unsaturated double bond include an acryloyl group, a methacryloyl group, an acryloyloxy group, a methacryloyloxy group, a vinyl group, a vinylphenyl group, and an allyl group.

[0048] Examples of the cyclic ether group include an epoxy group and an oxetanyl group.

[0049] An example of a nitrogen-containing heterocyclic group capable of undergoing a ring-opening reaction is an aziridinyl group.

[0050] The polymerizable group is preferably at least one selected from the group consisting of a group having an ethylenically unsaturated double bond and a cyclic ether group. Specifically, the polymerizable group is preferably at least one selected from the group consisting of an acryloyl group, a methacryloyl group, an acryloyloxy group, a methacryloyloxy group, a vinyl group, a vinylphenyl group, an allyl group, an epoxy group, an oxetanyl group, and an aziridinyl group, more preferably at least one selected from the group consisting of an acryloyl group, a methacryloyl group, an acryloyloxy group, and a methacryloyloxy group, and particularly preferably at least one selected from the group consisting of an acryloyloxy group and a methacryloyloxy group.

[0051] Liquid crystal compounds are classified into, for example, rod-shaped liquid crystal compounds and discotic liquid crystal compounds according to their chemical structures. Rod-shaped liquid crystal compounds are known as liquid crystal compounds having a rod-shaped chemical structure. As the rod-shaped liquid crystal compound, for example, known rod-shaped liquid crystal compounds can be used. As the discotic liquid crystal compound, for example, known discotic liquid crystal compounds can be used.

[0052] From the viewpoint of adjusting the optical properties (particularly the light diffraction properties) of the cholesteric liquid crystal film, the liquid crystal compound is preferably a rod-shaped liquid crystal compound, more preferably a rod-shaped thermotropic liquid crystal compound.

[0053] A rod-shaped thermotropic liquid crystal compound is a compound that has a rod-shaped chemical structure and exhibits liquid crystallinity in a specific temperature range. As the rod-shaped thermotropic liquid crystal compound, for example, a known rod-shaped thermotropic liquid crystal compound can be used.

[0054] Examples of rod-shaped thermotropic liquid crystal compounds include those described in Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials 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, WO 95 / 22586, WO 95 / 24455, WO 97 / 00600, WO 98 / 23580, WO 98 / 52905, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-T-11-513019, JP-A-11-80081, JP-A-2001-328973, or JP-A-2007-279688. Examples of rod-shaped thermotropic liquid crystal compounds include the liquid crystal compound represented by general formula 1 in JP-A No. 2016-81035 and the compound represented by general formula (I) or general formula (II) in JP-A No. 2007-279688.

[0055] The rod-shaped thermotropic liquid crystal compound is preferably a compound represented by the following general formula (1).

[0056] [ka]

[0057] In general formula (1), Q 1 , and Q 2 each independently represents a polymerizable group; L 1 , L 2 , L 3 , and L 4 each independently represents a single bond or a divalent linking group; A 1 , and A 2 each independently represents a divalent hydrocarbon group having 2 to 20 carbon atoms, and M represents a mesogenic group.

[0058] In general formula (1), Q 1 , and Q 2Examples of the polymerizable group represented by Q include the polymerizable groups described above. 1 , and Q 2 The preferred embodiments of the polymerizable group represented by the formula (I) are the same as those of the polymerizable group described above.

[0059] In general formula (1), L 1 , L 2 , L 3 , and L 4 is preferably a divalent linking group selected from the group consisting of -O-, -S-, -CO-, -NR-, -CO-O-, -O-CO-O-, -CO-NR-, -NR-CO-, -O-CO-, -O-CO-NR-, -NR-CO-O-, and NR-CO-NR-. R in the above divalent linking group represents an alkyl group having 1 to 7 carbon atoms or a hydrogen atom.

[0060] In general formula (1), L 3 , and L 4 At least one of the groups is preferably —O—CO—O—.

[0061] In general formula (1), Q 1 -L 1 - and Q 2 -L 2 Each - is preferably independently CH2=CH-CO-O-, CH2=C(CH3)-CO-O-, or CH2=C(Cl)-CO-O-, and more preferably CH2=CH-CO-O-.

[0062] In general formula (1), A 1 , and A 2The divalent hydrocarbon group represented by the formula (I) is preferably an alkylene group having 2 to 12 carbon atoms, an alkenylene group having 2 to 12 carbon atoms, or an alkynylene group having 2 to 12 carbon atoms, and more preferably an alkylene group having 2 to 12 carbon atoms. The divalent hydrocarbon group is preferably linear. The divalent hydrocarbon group may contain oxygen atoms that are not adjacent to each other or sulfur atoms that are not adjacent to each other. The divalent hydrocarbon group may have a substituent. Examples of the substituent include halogen atoms (e.g., fluorine, chlorine, and bromine), a cyano group, a methyl group, and an ethyl group.

[0063] In general formula (1), the mesogenic group represented by M is a group that forms the main skeleton of the liquid crystal compound, contributing to the formation of liquid crystals. For the mesogenic group represented by M, reference can be made to the description in "Flussige Kristalle in Tabellen II" (VEB DeutscheVerlag fur Grundstoff Industrie, Leipzig, published in 1984) (particularly pages 7 to 16) and the description in "Liquid Crystal Handbook" (edited by the Liquid Crystal Handbook Editorial Committee, Maruzen, published in 2000) (particularly Chapter 3).

[0064] In general formula (1), specific examples of the structure of the mesogenic group represented by M include the structures described in paragraph

[0086] of JP-A No. 2007-279688.

[0065] In general formula (1), the mesogenic group represented by M is preferably a group containing at least one cyclic structure selected from the group consisting of aromatic hydrocarbon groups, heterocyclic groups, and alicyclic hydrocarbon groups, and more preferably a group containing an aromatic hydrocarbon group.

[0066] In general formula (1), the mesogenic group represented by M is preferably a group containing 2 to 5 aromatic hydrocarbon groups, and more preferably a group containing 3 to 5 aromatic hydrocarbon groups.

[0067] In general formula (1), the mesogenic group represented by M preferably contains 3 to 5 phenylene groups, and the phenylene groups are linked to each other via -CO-O-.

[0068] In general formula (1), the cyclic structure (for example, an aromatic hydrocarbon group, a heterocyclic group, or an alicyclic hydrocarbon group) contained in the mesogenic group represented by M may have a substituent. Examples of the substituent include an alkyl group having 1 to 10 carbon atoms (for example, a methyl group).

[0069] Specific examples of compounds represented by general formula (1) are shown below. However, the compounds represented by general formula (1) are not limited to the compounds shown below. In the chemical structures of the compounds shown below, "-Me" represents a methyl group.

[0070] [ka]

[0071] [ka]

[0072] Specific examples of the rod-shaped thermotropic liquid crystal compound are shown below: However, the rod-shaped thermotropic liquid crystal compound is not limited to the compounds shown below.

[0073] [ka]

[0074] The liquid crystal compound may be a synthetic product synthesized by a known method or a commercially available product. Commercially available liquid crystal compounds are available from, for example, Tokyo Chemical Industry Co., Ltd. and Fujifilm Wako Pure Chemical Industries, Ltd.

[0075] From the viewpoint of heat resistance, the content of the liquid crystal compound is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the total mass of the cholesteric liquid crystal film. There is no upper limit to the content of the liquid crystal compound. The content of the liquid crystal compound may be determined to be 100% by mass or less, relative to the total mass of the cholesteric liquid crystal film. When the cholesteric liquid crystal film contains components other than the liquid crystal compound, the content of the liquid crystal compound may be determined to be less than 100% by mass (preferably 98% by mass or less, or 95% by mass or less), relative to the total mass of the cholesteric liquid crystal film. The content of the liquid crystal compound is, for example, preferably 70% by mass or more and less than 100% by mass, more preferably 80% by mass to 98% by mass, and particularly preferably 90% by mass to 95% by mass, relative to the total mass of the cholesteric liquid crystal film.

[0076] (Other ingredients) The cholesteric liquid crystal film may contain components other than the liquid crystal compound (hereinafter referred to as "other components" in this paragraph). Examples of the other components include a chiral agent, a solvent, an alignment regulator, a polymerization initiator, a leveling agent, an alignment aid, and a sensitizer.

[0077] [Thickness of cholesteric liquid crystal film] There is no particular limitation on the thickness of the cholesteric liquid crystal film, and it may be determined depending on the application. From the viewpoint of film strength, the thickness of the cholesteric liquid crystal film is preferably 0.5 μm or more, more preferably 1 μm or more, and particularly preferably 2 μm or more. From the viewpoint of alignment accuracy, the thickness of the cholesteric liquid crystal film is preferably 30 μm or less, more preferably 25 μm or less, and particularly preferably 20 μm or less. The thickness of the cholesteric liquid crystal film is, for example, preferably 0.5 μm to 30 μm, more preferably 1 μm to 25 μm, and particularly preferably 2 μm to 20 μm.

[0078] The thickness of the cholesteric liquid crystal film is determined by the following method. The film thickness is measured at five points in a cross section observed with a microscope in the thickness direction. The arithmetic mean value of the measured values is taken as the thickness of the cholesteric liquid crystal film.

[0079] [Other Layers] The cholesteric liquid crystal film according to the present disclosure may have a laminate structure including, in addition to the cholesteric liquid crystal film, layers other than the cholesteric liquid crystal film. The types of the other layers are not limited as long as they do not deviate from the spirit of the present disclosure. Examples of the other layers include a substrate and an alignment layer.

[0080] (base material) The cholesteric liquid crystal film according to the present disclosure may have a laminated structure together with a substrate. The substrate is preferably a resin substrate. Examples of resin substrates include polyester-based substrates (e.g., polyethylene terephthalate and polyethylene naphthalate), cellulose-based substrates (e.g., diacetyl cellulose and triacetyl cellulose (abbreviation: TAC)), polycarbonate-based substrates, poly(meth)acrylic-based substrates (e.g., poly(meth)acrylate (e.g., polymethyl methacrylate)), polystyrene-based substrates (e.g., polystyrene and acrylonitrile-styrene copolymer), olefin-based substrates (e.g., polyethylene, polypropylene, polyolefins having a cyclic structure (e.g., a norbornene structure), and ethylene-propylene copolymer), polyamide-based substrates (e.g., polyvinyl chloride, nylon, and aromatic polyamide), polyimide-based substrates, polysulfone-based substrates, polyethersulfone-based substrates, polyetheretherketone-based substrates, polyphenylene sulfide-based substrates, vinyl alcohol-based substrates, polyvinylidene chloride-based substrates, polyvinyl butyral-based substrates, polyoxymethylene-based substrates, and epoxy resin-based substrates. The substrate may be a substrate containing two or more types of resins (i.e., a blend polymer).The substrate is preferably a cellulose-based substrate, and more preferably a substrate containing triacetyl cellulose.

[0081] From the viewpoints of manufacturability, manufacturing costs, and optical properties, the thickness of the substrate is preferably in the range of 30 μm to 150 μm, and more preferably in the range of 40 μm to 100 μm.

[0082] (Alignment layer) The cholesteric liquid crystal film according to the present disclosure may have a laminated structure in which an alignment layer is provided between the substrate and the cholesteric liquid crystal film.

[0083] The alignment layer may be, for example, a known alignment layer having a function of imparting an alignment control force to a liquid crystal compound. The alignment layer may be an alignment layer that generates an alignment function by applying an electric field, a magnetic field, or light irradiation.

[0084] The thickness of the alignment layer is preferably in the range of 0.1 μm to 10 μm, and more preferably in the range of 1 μm to 5 μm.

[0085] Examples of methods for forming the alignment layer include rubbing an organic compound (preferably a polymer), oblique deposition of an inorganic compound, and formation of a layer having microgrooves.

[0086] [Application] The cholesteric liquid crystal film according to the present disclosure is expected to be applied to diffraction gratings, polarizing elements, anti-reflection films, and the like.

[0087] <Method for manufacturing cholesteric liquid crystal film> The method for producing a cholesteric liquid crystal film according to the present disclosure is not limited as long as it is a method capable of producing a cholesteric liquid crystal film in which, as described above, a striped pattern of alternating dark and light areas and a folded structure of dark areas can be seen in the surface layer of one of the pair of main surfaces when observed under a microscope in a cross section in the thickness direction. An example of a method for producing a cholesteric liquid crystal film according to the present disclosure will be described below, but the present disclosure is not limited to this method.

[0088] The method for producing a cholesteric liquid crystal film according to the present disclosure includes a first step of applying a coating liquid containing a solvent, a liquid crystal compound, and a chiral agent onto a substrate to form a coating film, and a second step of applying shear force to the surface of the formed coating film with a blade, wherein the shear rate in the second step is 1000 s -1 That's all. Each step will be specifically described below.

[0089] [1st step] In the first step, a coating liquid containing a solvent, a liquid crystal compound, and a chiral agent is applied onto a substrate to form a coating film.

[0090] (base material) The substrate used in the first step may be, for example, the substrate described in the above section "Substrate." Preferred embodiments of the substrate used in the first step are the same as those described in the above section "Substrate." An alignment layer may be previously disposed on the surface of the substrate used in the first step.

[0091] (liquid crystal compound) As the liquid crystal compound contained in the coating liquid used in the first step, for example, the liquid crystal compounds described above in the section "Liquid Crystal Compound" can be used. Preferred embodiments of the liquid crystal compound contained in the coating liquid are the same as those described above in the section "Liquid Crystal Compound."

[0092] The coating liquid may contain one type of liquid crystal compound alone, or two or more types of liquid crystal compounds.

[0093] The content of the liquid crystal compound is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the mass of the solid content of the coating solution. The upper limit of the content of the liquid crystal compound may be determined depending on the content of components other than the liquid crystal compound. The content of the liquid crystal compound may be determined within a range of less than 100% by mass (preferably 98% by mass or less, or 95% by mass or less), based on the mass of the solid content of the coating solution.

[0094] (Chiral agent) The type of chiral agent is not limited. As the chiral agent, for example, a known chiral agent (for example, the chiral agent described in "Liquid Crystal Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN and STN, p. 199, edited by the 42nd Committee of the Japan Society for the Promotion of Science, 1989") can be used.

[0095] Many chiral agents contain asymmetric carbon atoms. However, chiral agents are not limited to compounds containing asymmetric carbon atoms. Chiral agents also include, for example, axially asymmetric compounds and planarly asymmetric compounds that do not contain asymmetric carbon atoms. Examples of axially asymmetric compounds or planarly asymmetric compounds include binaphthyl, helicene, paracyclophane, and derivatives thereof.

[0096] The chiral agent may have a polymerizable group. For example, a polymer having a constitutional unit derived from the chiral agent and a constitutional unit derived from the liquid crystal compound is obtained by reacting a chiral agent having a polymerizable group with a liquid crystal compound having a polymerizable group.

[0097] Examples of the polymerizable group in the chiral agent include the polymerizable groups described above in the section "Liquid Crystal Compound." Preferred embodiments of the polymerizable group in the chiral agent are the same as those described above in the section "Liquid Crystal Compound." The type of the polymerizable group in the chiral agent is preferably the same as the type of the polymerizable group in the liquid crystal compound.

[0098] Examples of chiral agents exhibiting strong twisting power include those described in JP 2010-181852 A, JP 2003-287623 A, JP 2002-80851 A, JP 2002-80478 A, and JP 2002-302487 A. For the isosorbide compounds described in the above-mentioned documents, isomannide compounds having a corresponding structure can also be used as the chiral agent. Furthermore, for the isomannide compounds described in the above-mentioned documents, isosorbide compounds having a corresponding structure can also be used as the chiral agent.

[0099] The content of the chiral agent is preferably 0.5% by mass to 10.0% by mass, more preferably 0.8% by mass to 3.0% by mass, and particularly preferably 1.0% by mass to 3.0% by mass, based on the solid mass of the coating liquid.

[0100] (solvent) The solvent is preferably an organic solvent. Examples of the organic solvent include amide solvents (e.g., N,N-dimethylformamide), sulfoxide solvents (e.g., dimethyl sulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbon solvents (e.g., benzene and hexane), alkyl halide solvents (e.g., chloroform, dichloromethane), ester solvents (e.g., methyl acetate and butyl acetate), ketone solvents (e.g., acetone, methyl ethyl ketone, and cyclohexanone), and ether solvents (e.g., tetrahydrofuran and 1,2-dimethoxyethane). The organic solvent is preferably at least one selected from the group consisting of alkyl halide solvents and ketone solvents, and more preferably a ketone solvent.

[0101] The coating liquid may contain one solvent alone or two or more solvents.

[0102] The content of solids in the coating liquid is preferably 25% by mass to 40% by mass, and more preferably 25% by mass to 35% by mass, relative to the total mass of the coating liquid.

[0103] (Other ingredients) The coating liquid used in the first step may contain components other than those described above, such as an alignment regulator, a polymerization initiator, a leveling agent, an alignment aid, and a sensitizer.

[0104] -Alignment control agent- Examples of the alignment regulator include the compounds described in paragraphs

[0012] to

[0030] of JP 2012-211306 A, the compounds described in paragraphs

[0037] to

[0044] of JP 2012-101999 A, the fluorine-containing (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of JP 2007-272185 A, and compounds described in detail, along with their synthesis methods, in JP 2005-099258 A. A polymer described in JP 2004-331812 A containing more than 50 mass% of polymerized units of a fluoroaliphatic group-containing monomer based on the total polymerized units may also be used as the alignment regulator.

[0105] The alignment control agent may also be a vertical alignment agent, such as the boronic acid compounds and / or onium salts described in JP-A-2015-38598 and the onium salts described in JP-A-2008-26730.

[0106] The content of the alignment-regulating agent is preferably more than 0% by mass and not more than 5.0% by mass, more preferably 0.3% by mass to 2.0% by mass, based on the solid mass of the coating liquid.

[0107] -Polymerization initiator- Examples of the polymerization initiator include a photopolymerization initiator and a thermal polymerization initiator. The polymerization initiator is preferably a photopolymerization initiator from the viewpoint of suppressing deformation of the substrate due to heat and deterioration of the coating liquid. Examples of the photopolymerization initiator include α-carbonyl compounds (e.g., compounds described in U.S. Pat. No. 2,367,661 or U.S. Pat. No. 2,367,670), acyloin ethers (e.g., compounds described in U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (e.g., compounds described in U.S. Pat. No. 2,722,512), polynuclear quinone compounds (e.g., compounds described in U.S. Pat. No. 3,046,127 or U.S. Pat. No. 2,951,758), and combinations of triarylimidazole dimers and p-aminophenyl ketones (e.g., compounds described in U.S. Pat. No. 3,555,562). No. 49367), acridine compounds (e.g., compounds described in JP-A-60-105667 or U.S. Pat. No. 4,239,850), phenazine compounds (e.g., compounds described in JP-A-60-105667 or U.S. Pat. No. 4,239,850), oxadiazole compounds (e.g., compounds described in U.S. Pat. No. 4,212,970), and acylphosphine oxide compounds (e.g., compounds described in JP-B-63-40799, JP-B-5-29234, JP-A-10-95788, or JP-A-10-29997).

[0108] The content of the polymerization initiator is preferably 0.5% by mass to 5.0% by mass, and more preferably 1.0% by mass to 4.0% by mass, based on the mass of the solid content of the coating liquid.

[0109] (Method for preparing coating solution) The method for preparing the coating liquid used in the first step is not limited. The coating solution can be prepared, for example, by mixing the above-mentioned components. Any known mixing method can be used as the mixing method. In the coating solution preparation method, the above-mentioned components may be mixed, and then the resulting mixture may be filtered.

[0110] [Application method] The method for applying the coating liquid is not limited. Examples of methods for applying the coating liquid include an extrusion die coater method, a curtain coating method, a dip coating method, a spin coating method, a print coating method, a spray coating method, a slot coating method, a roll coating method, a slide coating method, a blade coating method, a gravure coating method, and a wire bar method.

[0111] [Coating thickness] The thickness of the coating film (i.e., the amount of the coating solution applied) is not limited. The thickness of the coating film may be determined, for example, according to the desired thickness of the cholesteric liquid crystal film or the thickness of the coating film before the shear force described in the "Second Step" section below is applied.

[0112] [Second process] In the second step, a shear force is applied to the coating surface formed in the first step by a blade. The shear rate in the second step is 1000 s -1 That's all.

[0113] (Shear force applied by blade) In the method of applying shear force to the surface of the coating film using a blade, it is preferable to scrape off the surface of the coating film with the blade. In the above method, the thickness of the coating film may change before and after the application of shear force. The thickness of the coating film after the application of shear force by the blade may be 1 / 2 or less, or 1 / 3 or less, of the thickness of the coating film before the application of shear force. The thickness of the coating film after the application of shear force by the blade is preferably 1 / 4 or more of the thickness of the coating film before the application of shear force.

[0114] The material of the blade is not limited, and examples of the material of the blade include metal (e.g., stainless steel) and resin (e.g., Teflon (registered trademark) and polyetheretherketone (PEEK)).

[0115] The shape of the blade is not limited, and may be, for example, a plate shape.

[0116] The blade is preferably a metal plate-like member, from the viewpoint of easily applying shear force to the coating film.

[0117] The thickness of the tip of the blade that comes into contact with the coating film is preferably 0.1 mm or more, more preferably 1 mm or more, from the viewpoint of easily applying shear force to the coating film. There is no upper limit to the blade thickness. The blade thickness may be determined, for example, within the range of 10 mm or less.

[0118] (shear rate) The shear rate in the second step was 1000 s -1 More than 10000 seconds -1 More preferably, it is 30,000 seconds or more. -1 The upper limit of the shear rate is not particularly limited. The shear rate is, for example, 1.0 × 10 6 seconds -1 It may be determined within the following range.

[0119] The method for calculating the shear rate is explained below. For example, when shear force is applied using a blade, the shear rate can be calculated by "V / d," where "d" is the shortest distance between the blade and the substrate, and "V" is the transport speed of the coating film in contact with the blade (i.e., the relative speed between the coating film and the blade).

[0120] (Paint surface temperature) The surface temperature of the coating film to which shear force is applied may be determined according to the phase transition temperature of the liquid crystal compound contained in the coating film. The surface temperature of the coating film to which shear force is applied is preferably 50°C to 120°C, more preferably 60°C to 100°C. By adjusting the surface temperature of the coating film within the above range, a cholesteric liquid crystal film with high alignment precision can be obtained. The surface temperature of the coating film is measured using a radiation thermometer whose emissivity is calibrated using the temperature value measured with a non-contact thermometer. The surface temperature of the coating film is measured on the opposite side to the measurement surface (i.e., the back side) when there is no reflective object within 10 cm of the surface.

[0121] (Coating thickness) The thickness of the coating film before the shear force is applied is preferably 30 μm or less, more preferably in the range of 10 μm to 25 μm, from the viewpoint of forming a cholesteric liquid crystal film with high alignment precision.

[0122] From the viewpoint of forming a cholesteric liquid crystal film with high alignment accuracy, the thickness of the coating film after the shear force is applied is preferably 10 μm or less, more preferably 8 μm or less. There is no lower limit to the thickness of the coating film after the shear force is applied. The thickness of the coating film after the shear force is applied is preferably in the range of 5 μm or more.

[0123] [3rd step] The method for producing a cholesteric liquid crystal film according to the present disclosure preferably includes a third step between the first and second steps, in which the solvent content in the applied coating film is adjusted to a range of 50 mass % or less relative to the total mass of the coating film. By adjusting the content of the solvent in the coating film to a range of 50% by mass or less, a cholesteric liquid crystal film with high alignment precision can be formed.

[0124] In the third step, the solvent content in the coating film is preferably 40% by mass or less, more preferably 30% by mass or less, based on the total mass of the coating film. There is no lower limit for the solvent content in the coating film. The solvent content in the coating film may be 0% by mass or more, based on the total mass of the coating film. The solvent content in the applied coating film may be 10% by mass or more, from the viewpoint of easily suppressing deterioration of the surface condition of the applied coating film.

[0125] The solvent content in the coating film is measured by the bone-drying method. The specific procedure for the measurement is explained below. A sample taken from the coating film is dried at 60°C for 24 hours, and then the change in mass of the sample before and after drying (i.e., the difference between the mass of the sample after drying and the mass of the sample before drying) is determined. The above operation is performed three times, and the arithmetic average of the values obtained is taken as the solvent content.

[0126] In the third step, an example of a method for adjusting the content of the solvent in the coating film is drying.

[0127] The coating film can be dried using known drying means, such as an oven, a hot air blower, and an infrared (IR) heater.

[0128] In drying using a hot air blower, hot air may be blown directly onto the coating film, or onto the surface of the substrate opposite to the surface on which the coating film is disposed. A diffusion plate may also be installed to prevent the surface of the coating film from flowing due to the hot air.

[0129] Drying may be performed by suction. For example, a vacuum chamber equipped with an exhaust mechanism may be used for drying by suction. By suctioning the gas surrounding the coating film, the solvent content in the coating film can be reduced.

[0130] The drying conditions are not limited as long as the solvent content in the coating film can be adjusted to 50% by mass or less, and may be determined depending on, for example, the components contained in the coating film, the coating amount of the coating film, and the conveying speed.

[0131] [4th step] In the method for producing a cholesteric liquid crystal film according to the present disclosure, when the coating liquid contains a polymerizable compound (e.g., a liquid crystal compound having a polymerizable group, or a chiral agent having a polymerizable group), it is preferable to have a fourth step of curing the coating film to which shear force has been applied after the second step. In the fourth step, the coating film is cured, thereby fixing the molecular alignment of the liquid crystal compound.

[0132] Methods for curing the coating film include, for example, heating and irradiation with active energy rays. In the fourth step, from the viewpoint of production suitability, it is preferable to cure the coating film by irradiating the coating film to which a shear force has been applied with active energy rays.

[0133] Examples of active energy rays include α rays, γ rays, X-rays, ultraviolet rays, infrared rays, visible light, and electron beams. From the viewpoints of curing sensitivity and ease of equipment availability, ultraviolet rays are preferred as the active energy rays.

[0134] Examples of sources of ultraviolet light include lamps (e.g., tungsten lamps, halogen lamps, xenon lamps, xenon flash lamps, mercury lamps, mercury xenon lamps, and carbon arc lamps), lasers (e.g., semiconductor lasers, helium-neon lasers, argon ion lasers, helium-cadmium lasers, and YAG (Yttrium Aluminum Garnet) lasers), light-emitting diodes, and cathode ray tubes.

[0135] The peak wavelength of the ultraviolet light emitted from the ultraviolet light source is preferably 200 nm to 400 nm.

[0136] The amount of ultraviolet light exposure (also called cumulative light amount) is 100 mJ / cm 2 ~500mJ / cm 2 It is preferable that:

[0137] [Other processes] The method for producing a cholesteric liquid crystal film according to the present disclosure may include steps other than the steps described above. The method for producing a cholesteric liquid crystal film according to the present disclosure may include, for example, a step of forming an alignment layer on a substrate. The step of forming an alignment layer on a substrate is preferably carried out before the first step.

[0138] The method for producing a cholesteric liquid crystal film according to the present disclosure may be carried out by a roll-to-roll method. In the roll-to-roll method, for example, each step is carried out while continuously transporting a long substrate. The method for producing a cholesteric liquid crystal film according to the present disclosure may also be carried out using substrates transported one by one.

[0139] A method for producing a cholesteric liquid crystal film according to the present disclosure will be described with reference to Fig. 5. Fig. 5 is a schematic diagram showing an example of a method for producing a cholesteric liquid crystal film according to the present disclosure.

[0140] 5, the cholesteric liquid crystal film is produced by a roll-to-roll method. A long substrate F wound into a roll is transported in the direction of the arrow by a transport roll 500. The transport speed of the substrate F is preferably 10 m / min to 100 m / min.

[0141] The coating liquid is applied to the substrate F that has passed through the transport roll 500 by the coating device 100 (first step). The coating liquid contains a liquid crystal compound, a chiral agent, and a solvent. The coating of the coating liquid by the coating device 100 is carried out in the area where the substrate F is wound around the backup roll 600. A preferred embodiment of the backup roll 600 will be described below.

[0142] For example, hard chrome plating may be applied to the surface of the backup roll 600. The thickness of the plating is preferably 40 μm to 60 μm.

[0143] The surface roughness Ra of the backup roll 600 is preferably 0.1 μm or less.

[0144] The surface temperature of the backup roll 600 may be controlled within any temperature range by a temperature control means. The surface temperature of the backup roll 600 may be determined depending on the composition of the coating liquid, the curing performance of the coating liquid, and the heat resistance of the substrate. The surface temperature of the backup roll 600 is preferably, for example, 40°C to 120°C, and more preferably 40°C to 100°C. Examples of the temperature control means for the backup roll 600 include heating means and cooling means. Examples of the heating means include induction heating, water heating, and oil heating. Examples of the cooling means include cooling with cooling water.

[0145] The diameter of the backup roll 600 is preferably 100 mm to 1,000 mm, more preferably 100 mm to 800 mm, and particularly preferably 200 mm to 700 mm.

[0146] The wrap angle of the substrate F relative to the backup roll 600 is preferably 60° or more, and more preferably 90° or more. The upper limit of the wrap angle can be set to, for example, 180°. The "wrap angle" refers to the angle between the transport direction of the substrate when it contacts the backup roll and the transport direction of the substrate when it separates from the backup roll.

[0147] The coating liquid is applied to the substrate F by the coating device 100 to form a coating film, and then the coating film is dried by the drying device 200 (third step). The content of the solvent in the coating film is adjusted by drying the coating film.

[0148] After the coating film is dried by the drying device 200, the upper surface of the coating film that has passed through the transport roll 510 is scraped off with the blade 300, thereby applying shear force to the surface of the coating film (second step). The shear force is applied in the direction of transport of the coating film (i.e., the direction of transport of the substrate). The shear force is applied by the blade 300 in the region where the substrate F is wound around the backup roll 610.

[0149] The preferred embodiment of the backup roll 610 is the same as that of the backup roll 600. The surface temperature of the backup roll 610 is preferably 50°C to 120°C, and more preferably 60°C to 100°C, for example.

[0150] After applying shear force to the coating film, the coating film is irradiated with active energy rays from a light source 400 to cure the coating film (fourth step). The coating is cured to form a cholesteric liquid crystal film on the substrate. [Example]

[0151] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to the following examples.

[0152] Example 1 [Preparing the substrate] A long triacetyl cellulose (TAC) film (Fujifilm Corporation, refractive index: 1.48, thickness: 80 μm, width: 300 mm) was prepared as a substrate.

[0153] [Formation of alignment layer] A coating solution for forming an alignment layer was prepared by stirring a mixture containing pure water (96 parts by mass) and PVA-205 (4 parts by mass, Kuraray Co., Ltd., polyvinyl alcohol) in a container kept at 80°C. The coating solution for forming an alignment layer was applied to a substrate (triacetyl cellulose film) using a bar (number: 6), and then dried in an oven at 100°C for 10 minutes. By the above procedure, an alignment layer with a thickness of 2 μm was formed on the substrate.

[0154] [Formation of cholesteric liquid crystal film] A cholesteric liquid crystal film having a thickness of 8 μm was formed on the alignment layer by the following procedure.

[0155] (Preparation of Liquid Crystal Layer Forming Coating Solution (1)) The components shown below were mixed and then filtered using a polypropylene filter (pore size: 0.2 μm) to prepare a liquid crystal layer-forming coating solution (1).

[0156] -component- (1) Rod-shaped thermotropic liquid crystal compound (compound (A) below): 100 parts by mass (2) Chiral agent (compound (B) shown below, Palicolor (registered trademark) LC756, BASF): 1.2 parts by mass (3) Photopolymerization initiator 1 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, Omnirad 907, IGM Resins BV): 3 parts by mass (4) Photopolymerization initiator 2 (PM758, Nippon Kayaku Co., Ltd.): 1 part by mass (5) Alignment control agent (compound (C) below): 0.5 parts by mass (6) Solvent (methyl ethyl ketone): 184 parts by mass (7) Solvent (cyclohexanone): 31 parts by mass

[0157] Compound (A) is a mixture of the following three compounds, the contents of which in the mixture are, from top to bottom, 84 mass %, 14 mass %, and 2 mass %.

[0158] [ka]

[0159] The chemical structure of compound (B) is shown below.

[0160] [ka]

[0161] The chemical structure of compound (C) is shown below.

[0162] [ka]

[0163] (coating) The substrate having the alignment layer was heated at 70° C., and then the liquid crystal layer forming coating liquid (1) was applied onto the alignment layer using a bar (number: 18).

[0164] (Dry) The liquid crystal layer forming coating solution (1) applied onto the alignment layer was dried in an oven at 70° C. for 1 minute to form a coating film with a thickness of 10 μm.

[0165] (Application of shear force) The coating film was heated to 70°C, and a stainless steel blade heated to 70°C was brought into contact with the coating film. The blade was then moved at a speed of 1.5 m / min while still in contact with the coating film, thereby applying a shear rate of 2500 s -1 The blade travel distance was 30 mm. The residual solvent content of the coating film subjected to shearing was less than 1% by mass. The thickness of the coating film after the shear force was applied was 8 μm.

[0166] (hardening) The coating film was subjected to shear stress and exposed to ultraviolet light (exposure dose: 500 mJ / cm) using a metal halide lamp. 2 The coating was cured by irradiating it with light.

[0167] <Example 2> The cholesteric liquid crystal film of Example 2 was produced by the same procedure as in Example 1, except that the liquid crystal layer-forming coating solution (2) was used, in which the rod-shaped thermotropic liquid crystal compound was changed to the following compound (D).

[0168] The chemical structure of compound (D) is shown below.

[0169] [ka]

[0170] Example 3 A liquid crystal layer-forming coating solution (3) was prepared in the same manner as in Example 1, except that the following components were used.

[0171] -component- (1) Rod-shaped thermotropic liquid crystal compound (compound (A)): 100 parts by mass (2) Chiral agent (compound (E) below): 1.2 parts by mass (3) Photopolymerization initiator 2 (PM758, Nippon Kayaku Co., Ltd.): 3 parts by mass (4) Photopolymerization initiator 3 (IRGANOX (registered trademark) 1010, BASF): 1 part by mass (5) Alignment control agent (compound (C)): 0.5 parts by mass (6) Solvent (methyl ethyl ketone): 184 parts by mass (7) Solvent (cyclohexanone): 31 parts by mass

[0172] The chemical structure of compound (E) is shown below.

[0173] [ka]

[0174] Subsequently, a cholesteric liquid crystal film of Example 3 was produced using the obtained liquid crystal layer-forming coating liquid (3) in the same manner as in Example 1, except that curing was carried out as described below.

[0175] (hardening) The coating film to which shear stress was applied was exposed to ultraviolet light (exposure dose: 5 mJ cm) from a high-pressure mercury lamp (HOYA Corporation, UL750) through a long-wavelength cut filter (Asahi Spectroscopy Co., Ltd., SH0325). 2 The coating was cured by irradiation with UV light. FIG. 1 is a photograph of the cholesteric liquid crystal film of Example 1, taken from the top surface (surface) of the liquid crystal film, using a polarizing microscope.

[0176] <Comparative Example 1> The cholesteric liquid crystal film of Comparative Example 1 was produced by the same procedure as in Example 1, except that the thickness of the coating film obtained after drying (i.e., the thickness of the coating film before the application of shear force) was changed to 25 μm, and then the shear force described below was applied. FIG. 6 shows a photograph of the cholesteric liquid crystal film of Comparative Example 1 observed from the top (surface) with a polarizing microscope.

[0177] (Application of shear force) With the coating film heated to 110°C, a stainless steel blade heated to 110°C was brought into contact with the coating film, and then, while still in contact with the coating film, the blade was moved at a speed of 0.9 m / min, thereby applying a shear rate of 600 s-1 The blade travel distance was 30 mm. The thickness of the coating film after the shear force was applied was 22 μm.

[0178] <Comparative Example 2> A cholesteric liquid crystal film of Comparative Example 2 was produced in the same manner as in Example 1, except that the dried coating film was cured without applying shear force to the coating film. FIG. 7 shows a photograph of the cholesteric liquid crystal film of Comparative Example 2 observed from the top (surface) with a polarizing microscope. As is clear from FIG. 7, the cholesteric liquid crystal film of Comparative Example 2 does not show a striped pattern of alternating dark and light areas in straight lines when viewed from the top (surface) using a polarizing microscope.

[0179] [Microscopic observation of the top surface and cross section in the thickness direction] A photograph was taken from the top surface of the obtained cholesteric liquid crystal film using a polarizing microscope NV100LPOL manufactured by Nikon Corporation, and linear stripe patterns were observed from the photographic image. The microscope observation from above was carried out on both the front surface (here, the surface to which shear was applied) and the back surface (here, the surface in contact with the substrate) of the cholesteric liquid crystal film. The obtained cholesteric liquid crystal film was cut with a microtome, and a cross-section was photographed using a polarizing microscope NV100LPOL manufactured by Nikon Corporation, and a cross-sectional stripe pattern was observed from the cross-section photograph image. The distance between dark areas, the number of connection points, and the tilt angle of the dark areas were also determined. The results are shown in Table 1. In Comparative Example 1, no linear stripes were observed when observed from above (front and back surfaces), so the distance between dark areas and the number of connecting points were not determined.

[0180] [Periodic change in refractive index] When observing the top surface of a cholesteric liquid crystal film under a microscope, the appearance of a highly linear stripe pattern indicates that the helical structure of the cholesteric liquid crystal, with approximately the same period, is regularly aligned along a straight line. Within the helical structure of the cholesteric liquid crystal with the same period, the molecular axes of the liquid crystal compound are arranged in a similar spirally twisted manner. Since the refractive index of a cholesteric liquid crystal film changes depending on the direction of the molecular axes of the liquid crystal compound on the top surface, as described above, the appearance of a highly linear stripe pattern when observing the top surface of a cholesteric liquid crystal film under a microscope indicates that the refractive index is changing periodically along the stripe pattern. From the above, it can be said that the cholesteric liquid crystal films of Examples 1 to 3 have linear striped patterns, and therefore the refractive index changes periodically.

[0181] [Table 1]

[0182] As is clear from Table 1, when the cholesteric liquid crystal film of the example was observed from above with a microscope, a striped pattern in which dark and light areas were alternately arranged in straight lines was observed. Furthermore, when the cholesteric liquid crystal film of the example was observed under a microscope in a cross section in the thickness direction, a striped pattern in which dark and light areas were alternately arranged was observed.

[0183] [Explanation of symbols] 1 Cholesteric liquid crystal film 10 dark side 20 Akabe 30 connection points 40 Rod-shaped liquid crystal compound 40A molecular axis 100 Coating equipment 200 Drying equipment 300 blades 400 light sources 500, 510 transport roll 600, 610 backup roll F Base material Fa, Fb principal surfaces HA Helical axis θ is the angle of inclination of the dark area in the cross-sectional stripe pattern relative to the principal plane

[0184] The disclosure of Japanese Patent Application No. 2020-015749, filed on January 31, 2020, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. comprising a cholesteric liquid crystal; and When observed under a microscope, the top surface had a striped pattern of alternating dark and light areas. The distance between adjacent dark areas is 0.01 μm to 50 μm, the upper surface is a main surface of the cholesteric liquid crystal film, and the main surface is a surface having a major area among the surfaces of the cholesteric liquid crystal film; A cholesteric liquid crystal film having an upper surface, when observed under a microscope, having bonding points where dark areas are bonded to each other, and the number of said bonding points per 50 μm square area is 1 to 3.

2. comprising a cholesteric liquid crystal; and When observed under a microscope, the top surface had a striped pattern of alternating dark and light areas. the upper surface is a main surface of the cholesteric liquid crystal film, and the main surface is a surface having a major area among the surfaces of the cholesteric liquid crystal film; the principal surfaces form a pair of principal surfaces corresponding to the front and back surfaces of a cholesteric liquid crystal film, When observed under a microscope, the upper surface has bonding points where the dark areas are bonded together. A cholesteric liquid crystal film, wherein the number of bonding points per 50 μm square area is different between the pair of principal surfaces.

3. 3. The cholesteric liquid crystal film according to claim 2, wherein the distance between adjacent dark portions is 0.01 μm to 50 μm.

4. 4. The cholesteric liquid crystal film according to claim 1, wherein a cross section in the thickness direction observed under a microscope has a striped pattern in which dark and light areas are alternately arranged, and the dark areas are inclined with respect to the main surface.

5. 5. The cholesteric liquid crystal film according to claim 4, wherein the dark portions have an inclination angle of 20° to 90° with respect to the principal surface.

6. A coating solution containing a solvent, a liquid crystal compound, and a chiral agent is applied onto a substrate to form a coating film. One process and a second step of applying shear force to the formed coating surface with a blade; and the surface temperature of the formed coating film is 50°C to 120°C, The shear rate in the second step is 2500 s －１ This completes the method for producing a cholesteric liquid crystal film.

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