Optical film

Abstract

To prevent a damage on an external appearance of an optical film while appropriately orienting a cholesteric liquid crystal.SOLUTION: An optical film 10 includes a liquid crystal layer 30 including a cholesteric liquid crystal 35. A rugged shape 32 is formed on a first face 31 of the liquid crystal layer 30. In a double logarithmic chart of a power spectral density to a spacial frequency of the rugged shape 32, a value of ratio α / β of a tilt α of a regression line within a range of spacial frequency 0.01 / μm to 0.1 / μm to a tilt β of a regression line within a range of spacial frequency 0.1 / μm to 1 / μm is 0.38 to 0.72.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to optical films. [Background technology]

[0002] An optical film having a liquid crystal layer as described in Patent Document 1 is known. The liquid crystal layer contains cholesteric liquid crystal. By orienting the cholesteric liquid crystal in a helical shape, the liquid crystal layer reflects circularly polarized light in a direction corresponding to the rotation direction of the cholesteric liquid crystal helix and light of a wavelength corresponding to the pitch of one turn of the helix. By controlling the rotation direction of the helix and the pitch of the helix in which the cholesteric liquid crystal is oriented in the manufacturing process of the liquid crystal layer, a liquid crystal layer that reflects circularly polarized light of a desired wavelength can be manufactured. The liquid crystal layer is manufactured to reflect, for example, infrared rays. An optical film having a liquid crystal layer that reflects infrared rays can be used as an infrared reflective material used for heat insulation, for example.

[0003] A rubbed alignment film is used to align the cholesteric liquid crystal, which then becomes helically aligned.

[0004] Cholesteric liquid crystal can be aligned without an alignment film. Cholesteric liquid crystal can be aligned by forming an uneven shape on the surface of the substrate supporting the liquid crystal layer. By producing an optical film without an alignment film, the optical film can be made thin, and the manufacturing process of the optical film can be simplified. The manufacturing cost of the optical film can be reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-233987 A Summary of the Invention [Problem to be solved by the invention]

[0006] When an uneven shape is formed on the surface of the substrate, an uneven shape is also formed on the surface of the liquid crystal layer supported by the substrate. These uneven shapes can adversely affect the appearance of the optical film. The present disclosure aims to suppress deterioration of the appearance while appropriately aligning cholesteric liquid crystals. [Means for solving the problem]

[0007] One embodiment of the present disclosure relates to the following [1] to [6]. [1] A liquid crystal layer including a cholesteric liquid crystal, A concave-convex shape is formed on a first surface of the liquid crystal layer, an optical film, in which in a log-log graph of power spectral density versus spatial frequency of the uneven shape, a ratio α / β of a slope α of a regression line in the spatial frequency range of 0.01 / μm to a slope β of a regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 or more and 0.72 or less. [2] A liquid crystal layer including a cholesteric liquid crystal, A concave-convex shape is formed on a first surface of the liquid crystal layer, an optical film, in which in a log-log graph of power spectral density versus spatial frequency of the uneven shape, the difference β-α between the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is -0.81 or more and -0.22 or less. [3] A substrate and a liquid crystal layer laminated on a second surface of the substrate, the liquid crystal layer includes a cholesteric liquid crystal; A second uneven shape is formed on the second surface, An optical film, in which in a log-log graph of power spectral density versus spatial frequency of the second uneven shape, the ratio α / β of the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm to the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 or more and 0.72 or less. [4] A substrate and a liquid crystal layer laminated on a second surface of the substrate, the liquid crystal layer includes a cholesteric liquid crystal; A second uneven shape is formed on the second surface, An optical film, in which in a log-log graph of power spectral density versus spatial frequency of the second uneven shape, the difference β-α between the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is -0.81 or more and -0.22 or less. [5] a first surface of the liquid crystal layer facing the second surface of the base material; The optical film according to [3] or [4], wherein the first surface has an uneven shape formed thereon that fits with the second uneven shape. [6] The optical film according to any one of [1] to [5], wherein the liquid crystal layer reflects circularly polarized infrared light. Effect of the Invention

[0008] According to the present disclosure, it is possible to appropriately align cholesteric liquid crystals while preventing the appearance of the optical film from being easily impaired. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is an exploded cross-sectional view showing an optical film according to an embodiment. [Diagram 2] FIG. 2 is a perspective view that illustrates a schematic view of cholesteric liquid crystal in the liquid crystal layer. [Diagram 3] FIG. 3 is a log-log graph of the power spectral density versus spatial frequency of the concave-convex shape. [Figure 4] FIG. 4 is an exploded perspective view showing a modified example of the optical film. [Diagram 5] FIG. 5 is an exploded perspective view showing another modified example of the optical film. [Figure 6] FIG. 6 is a double logarithmic graph of the power spectral density versus spatial frequency of the concave-convex shape of a conventional optical film. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the present disclosure will be described with reference to the drawings. In the drawings accompanying this specification, the scale and aspect ratios may be appropriately changed and exaggerated from those of the actual objects in order to facilitate illustration and understanding.

[0011] As used in this specification, terms specifying shapes and geometric conditions and their degrees, such as "parallel," "orthogonal," and "same," as well as values ​​of lengths and angles, are not limited to their strict meanings and are interpreted to include a range within which similar functions can be expected.

[0012] 1 is an exploded cross-sectional view of an optical film 10 according to an embodiment of the present disclosure. The optical film 10 functions as, for example, a reflector that reflects light of a specific wavelength. The optical film 10 is a thin-film member. The thickness of the optical film 10 is, for example, 19.5 μm or more and 270 μm or less.

[0013] 1, the optical film 10 includes a substrate 20 and a liquid crystal layer 30. The optical film 10 may further include a bonding layer (not shown) that bonds the substrate 20 and the liquid crystal layer 30 together.

[0014] The substrate 20 supports the liquid crystal layer 30. The substrate 20 is a transparent film-like member. The substrate 20 has an appropriate thickness to support the liquid crystal layer 30 and to prevent the optical film 10 from becoming too thick. The thickness of the substrate 20 is, for example, 19 μm or more and 250 μm or less. The material of the substrate 20 is, for example, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, or cyclic polyolefin.

[0015] An irregular second uneven shape 22 is formed on a second surface 21, which is one of the main surfaces of the base material 20. The second uneven shape 22 may be formed by including a filler (not shown) in the base material 20, or may be formed by shaping the base material 20 in a mold having a shape corresponding to the desired uneven shape.

[0016] FIG. 2 is a schematic perspective view of the liquid crystal layer 30. As shown in FIG. 2, the liquid crystal layer 30 includes a plurality of cholesteric liquid crystals 35. In FIG. 2, several cross sections at various positions in the thickness direction of the liquid crystal layer 30 are shown. As shown in FIG. 2, the cholesteric liquid crystals 35 are helically oriented in the thickness direction of the liquid crystal layer 30. The liquid crystal layer 30 reflects light that is circularly polarized in a direction corresponding to the rotation direction of the spiral of the cholesteric liquid crystals 35 and has a wavelength corresponding to the pitch length of one turn of the spiral. The rotation direction of the spiral of the cholesteric liquid crystals 35 may be either rightward or leftward. The spiral pitch of the cholesteric liquid crystals 35 has a length corresponding to the wavelength of infrared light or visible light. As a specific example, the spiral pitch length of one turn of the cholesteric liquid crystals 35 is 100 nm or more and 1000 nm or less. The liquid crystal layer 30 reflects infrared light or visible light that is circularly polarized in a direction corresponding to the rotation direction of the spiral of the cholesteric liquid crystals 35. The reflectance of the liquid crystal layer 30 for light that is circularly polarized in a direction corresponding to the direction of rotation of the helix of the cholesteric liquid crystal 35 and has a wavelength corresponding to the pitch length of one turn of the helix of the cholesteric liquid crystal 35 is, for example, 25% or more and 50% or less.

[0017] The reflectance is calculated from the total amount of reflected light, which is the sum of the regular reflection component and the diffuse reflection component. The reflectance is measured using a reflectance meter (V-670 and integrating sphere unit ISN-723 manufactured by JASCO Corporation). Light of a specific wavelength is irradiated from a direction at 45 degrees to the normal direction of the optical film, and the ratio of the total amount of reflected light, which is the sum of the regular reflection component and the diffuse reflection component of the reflected light, to the amount of incident light, expressed as a percentage, is the reflectance at that wavelength.

[0018] The liquid crystal layer 30 is a thin-film member. The liquid crystal layer 30 is laminated on the second surface 21 of the substrate 20. A first surface 31, which is one of the main surfaces of the liquid crystal layer 30, faces the second surface 21 of the substrate 20. The liquid crystal layer 30 is in contact with the substrate 20. The first surface 31 is in contact with the second surface 21. An irregular uneven shape 32 is formed on the first surface 31 by transferring the second uneven shape 22 of the second surface 21 of the substrate 20. The uneven shape 32 has a shape complementary to the second uneven shape 22. The uneven shape 32 fits into the second uneven shape 22. The uneven shape 32 formed on the first surface 31 aligns the cholesteric liquid crystal 35 in the liquid crystal layer 30.

[0019] The cholesteric liquid crystal material is, for example, a mixture of a commercially available liquid crystal composition and a chiral agent. Cholesteric liquid crystal is obtained by blending a chiral agent with a molecular material that exhibits a plurality of liquid crystal properties.

[0020] An example of a method for producing the optical film 10 will be described.

[0021] The substrate 20 is prepared so that the second uneven shape 22 is formed. For example, the substrate 20 having the second uneven shape 22 formed thereon is prepared by including a filler of an appropriate size so that the desired uneven shape is formed in the resin composition that becomes the substrate 20. Alternatively, the substrate 20 having the second uneven shape 22 formed thereon is prepared by shaping the resin composition that becomes the substrate 20 with a mold having a shape corresponding to the desired uneven shape. Alternatively, the substrate 20 having the second uneven shape 22 formed thereon is prepared by adjusting the stretching processing conditions of the resin composition that becomes the substrate 20. The substrate 20 may be prepared by a combination of these. The substrate 20 having the second uneven shape 22 formed thereon may be prepared by other methods.

[0022] A liquid crystal layer 30 is formed on the second surface 21 of the substrate 20. A coating film containing a rod-shaped compound having a polymerizable functional group in the molecule and capable of forming a cholesteric structure and a chiral agent that imparts a rotational property in a first direction is formed on the second surface 21 of the substrate 20. Here, the first direction is either the right direction or the left direction. The chiral agent is adjusted so that the length of one rotation of the cholesteric structure to be formed corresponds to the wavelength reflected by the liquid crystal layer 30 to be formed. By drying the coating film, the rod-shaped compound forms a cholesteric structure with the chiral agent, and a coating film having a rotational property in the first direction is formed. By irradiating the coating film with ultraviolet light or the like, the rod-shaped compound is polymerized. The coating film is hardened to form a liquid crystal layer 30 containing cholesteric liquid crystal 35 having a helical structure rotated in the first direction.

[0023] The liquid crystal layer 30 is formed on the second surface 21 of the substrate 20, thereby producing the optical film 10. By continuously performing the above-mentioned steps, a sufficiently long optical film 10 can be produced. For example, an optical film 10 having a long side of 100 m or more and 9000 m or less can be produced. The sufficiently long optical film 10 is wound up in a roll. The optical film 10 is used by cutting it to a desired size.

[0024] Conventionally, an uneven shape is formed on the surface of the substrate of an optical film. By forming an appropriate uneven shape on the surface of the substrate, an uneven shape is also formed on the surface of the liquid crystal layer. The uneven shape on the surface of the liquid crystal layer aligns the cholesteric liquid crystal without an alignment film.

[0025] The appearance of conventional optical films was sometimes deteriorated. The inventors of the present invention have found that the uneven surface shape of the substrate or liquid crystal layer deteriorates the appearance of the optical film. Specifically, when the optical film is irradiated with light, the uneven surface shape causes the light to scatter. Due to the scattered light, the optical film was observed to have sand-like unevenness. In particular, when a sufficiently large optical film is formed to efficiently manufacture the optical film, the appearance of the entire optical film is not stable. Specifically, in an optical film with a long side of 100 m or more and 9000 m or less, the appearance of the entire optical film is not stable.

[0026] In order to suppress the deterioration of the appearance of the optical film while properly aligning the cholesteric liquid crystal, it was considered to specify the roughness of the uneven shape. Specifically, it was considered to specify the arithmetic mean roughness or the ten-point mean roughness of the surface of the substrate or the liquid crystal layer. However, even if the roughness of the uneven shape is specified, the cholesteric liquid crystal may not be properly aligned, and the deterioration of the appearance of the optical film may not be suppressed. Even if the roughness of the uneven shape is specified, it is not possible to stably align the cholesteric liquid crystal while stably suppressing the deterioration of the appearance of the optical film. The present inventors have studied and found that the alignment of the cholesteric liquid crystal and the suppression of the deterioration of the appearance of the optical film can be evaluated by the spatial frequency of the uneven shape, not by the roughness due to the uneven shape.

[0027] In this embodiment, in order to evaluate the spatial frequency of the uneven shape, the power spectral density with respect to the spatial frequency of the uneven shape 32 formed on the first surface 31 of the liquid crystal layer 30 and the second uneven shape 22 formed on the second surface 21 of the substrate 20 is considered. Since the uneven shape 32 and the second uneven shape 22 are complementary shapes, their power spectral densities with respect to the spatial frequency are the same. In the following, the power spectral density with respect to the spatial frequency of the uneven shape 32 is considered, but the same idea also applies to the power spectral density with respect to the spatial frequency of the second uneven shape 22.

[0028] A method of obtaining the power spectrum density for the spatial frequency of the uneven shape 32 will be described. The first surface 31 of the liquid crystal layer 30 is cut out so as to be a rectangle with a side length of 15 mm to 20 mm. A part of the cut out liquid crystal layer 30 is fixed to a slide glass with tape. The first surface 31 of the liquid crystal layer 30 fixed to the slide glass is scanned with a laser microscope (VK-X150 manufactured by KEYENCE). The laser microscope is set to scan the outermost surface of a transparent body with an objective lens of 50 times and an optical zoom of 1.0 times. The scanning pitch is less than 1 μm, for example, 0.13 μm. This allows data obtained by scanning the shape of the first surface 31 of the liquid crystal layer 30 to be obtained. The data is corrected taking into consideration that the first surface 31 of the liquid crystal layer 30 is inclined with respect to the horizontal plane during scanning. Of the corrected data, data in the height direction with respect to the scanning direction is extracted for one direction parallel to the short side of the cut out liquid crystal layer 30. The number of data extracted for one direction is, for example, 1024 to 4096. The data in the height direction relative to the scanning direction is data on the shape of the uneven shape 32. By subjecting the data on the shape of the uneven shape 32 to a discrete Fourier transform, the power spectrum density for the spatial frequency of the uneven shape 32 can be obtained.

[0029] FIG. 3 is an example of a log-log graph of the power spectrum density versus the spatial frequency of the uneven shape 32. The graph shown in FIG. 3 corresponds to Example 2 described later. As a method for evaluating the spatial frequency, the slope of the log-log graph, which is one of the features of the spatial frequency, is used. In this embodiment, the spatial frequency of the uneven shape 32 is evaluated by the slope of the regression line in the log-log graph in the range of spatial frequencies from 0.01 / μm to 0.1 / μm and in the range of spatial frequencies from 0.1 / μm to 1 / μm. The range of spatial frequencies from 0.01 / μm to 0.1 / μm represents a frequency component with a relatively long period in the uneven shape 32. It is presumed that this represents the ease with which the uneven shape is visually recognized when light is incident and the ease with which the orientation of the cholesteric liquid crystal is disturbed. The range of spatial frequencies from 0.1 / μm to 1 / μm represents a frequency component with a relatively short period in the uneven shape 32. It is presumed that this is related to the interference caused by the uneven shape when light is incident and the stability of the alignment of the cholesteric liquid crystal inside the liquid crystal layer, however, the present embodiment is not limited to the above presumption.

[0030] As a result of the study by the present inventors, it was found that when the value of the ratio α / β of the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm to the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 to 0.72, it is possible to suppress the deterioration of the appearance of the optical film while aligning the cholesteric liquid crystal. Alternatively, when the value of the difference β-α between the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is -0.81 to -0.22, it was found that the deterioration of the appearance of the optical film 10 can be suppressed while aligning the cholesteric liquid crystal 35 in the liquid crystal layer 30. In particular, even in the optical film 10 with a long side of 100 m or more, it is possible to suppress the deterioration of the appearance of the optical film 10 while aligning the cholesteric liquid crystal 35 over the entire optical film 10.

[0031] In conventional optical films, the spatial frequency of the uneven shape was not evaluated, which may have led to failure to align the cholesteric liquid crystal or failure to suppress deterioration of the appearance of the optical film. In particular, conventionally, it has not been possible to stably suppress deterioration of the appearance of the optical film while properly aligning the cholesteric liquid crystal over the entire optical film 10, which has a sufficiently long long side of 100 m or more.

[0032] In considering this embodiment, the spatial frequency of the concave-convex shape of a conventional optical film was evaluated. Figure 6 shows an example of a double logarithmic graph of the power spectrum density versus the spatial frequency of the concave-convex shape of a conventional optical film. The graph shown in Figure 6 corresponds to Comparative Example 2, which will be described later.

[0033] The optical film 10 of the present embodiment includes a liquid crystal layer 30 including a cholesteric liquid crystal 35. A concave-convex shape 32 is formed on a first surface 31 of the liquid crystal layer 30. In a double logarithmic graph of the power spectrum density versus spatial frequency of the concave-convex shape 32, the ratio α / β of the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm to the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 or more and 0.72 or less. Alternatively, in a double logarithmic graph of the power spectrum density versus spatial frequency of the concave-convex shape 32, the difference β-α between the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is -0.81 or more and -0.22 or less. According to the optical film 10 of the present embodiment, the concave-convex shape 32 can align the cholesteric liquid crystal 35. This can prevent the unevenness 32 from deteriorating the appearance of the optical film 10 .

[0034] Alternatively, the optical film 10 of the present embodiment includes a substrate 20 and a liquid crystal layer 30 laminated on a second surface 21 of the substrate 20. The liquid crystal layer 30 contains cholesteric liquid crystals 35. A second uneven shape 22 is formed on the second surface 21. In a double logarithmic graph of the power spectral density versus spatial frequency of the second uneven shape 22, the ratio α / β of the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm to the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 or more and 0.72 or less. Alternatively, in a log-log graph of the power spectral density versus spatial frequency of the second uneven shape 22, the difference β-α between the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is −0.81 or more and −0.22 or less. According to the optical film 10 of the present embodiment, the second uneven shape 22 forms the uneven shape 32 in the liquid crystal layer 30, and the cholesteric liquid crystal 35 can be aligned. The deterioration of the appearance of the optical film 10 due to the second uneven shape 22 can be suppressed.

[0035] Various modifications can be made to the above-described embodiment.

[0036] 4 shows a modified example of the optical film 10. As in the example shown in FIG. 4, the optical film 10 may further include a second liquid crystal layer 40. The second liquid crystal layer 40 reflects circularly polarized light having a direction opposite to the direction of circular polarization of the light reflected by the liquid crystal layer 30. The second liquid crystal layer 40 may have the same configuration as the liquid crystal layer 30, except that the helical rotation direction of the cholesteric liquid crystal is opposite to the helical rotation direction of the cholesteric liquid crystal 35 of the liquid crystal layer 30.

[0037] In the example shown in FIG. 4, the base material 20 has a fourth uneven shape 24 formed on a fourth surface 23, which is the main surface opposite to the second surface 21. A third surface 41, which is the main surface of the second liquid crystal layer 40, faces the fourth surface 23 of the base material 20. A third uneven shape 42 is formed on the third surface 41. The third uneven shape 42 has a shape complementary to the fourth uneven shape 24. The third uneven shape 42 fits into the fourth uneven shape 24. The third uneven shape 42 aligns the cholesteric liquid crystal of the second liquid crystal layer 40.

[0038] By including the second liquid crystal layer 40, the optical film 10 can reflect light having a wavelength corresponding to the pitch of one turn of the helix that is circularly polarized in either the left or right direction, and can function as a reflective material that reflects light of a specific wavelength.

[0039] Fig. 5 shows another modified example of the optical film 10. As in the example shown in Fig. 5, the optical film 10 may further include a quarter-wave plate 50. The quarter-wave plate 50 generates a phase modulation of a quarter wavelength in light having a wavelength corresponding to the pitch of one helix turn of the cholesteric liquid crystal 35 of the liquid crystal layer 30. The quarter-wave plate 50 can change linearly polarized light into circularly polarized light and can change circularly polarized light into linearly polarized light.

[0040] The inclusion of the quarter wave plate 50 allows the optical film 10 to function as a polarizer that transmits only one polarized component of light of a specific wavelength and reflects the other polarized component. By reflecting the light reflected by the optical film 10 again for use, the light can be used without loss. When the light of the specific wavelength is particularly visible light, the optical film 10 is used as a polarizer for use in, for example, a liquid crystal display device.

[0041] 1, 3, and 4, the substrate 20 may be omitted. For example, the substrate 20 may be peeled off from the liquid crystal layer 30 by a peeling layer (not shown). EXAMPLES

[0042] The present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the examples.

[0043] As examples and comparative examples, optical films having a substrate and a liquid crystal layer containing cholesteric liquid crystal were prepared. In each example and comparative example, the substrate was prepared by changing the surface shape of Toyobo's E5100 made of polyethylene terephthalate under different conditions. In order to change the surface shape of the substrate, for example, the amount of filler contained in the resin composition to be the substrate was changed, and / or the shape of the mold for shaping the resin composition to be the substrate was changed, and / or the stretching processing conditions of the resin composition to be the substrate were changed. By changing the preparation conditions of the substrate, the second uneven shape formed on the second surface of the substrate was different between the optical films of each example and comparative example. Accordingly, the uneven shape of the first surface of the liquid crystal layer was also different between the optical films of each example and comparative example.

[0044] On the prepared substrate, a coating film was formed containing a rod-shaped compound that has a polymerizable functional group in the molecule and can form a cholesteric structure, and a chiral agent that imparts rotation in a certain direction. The chiral agent is adjusted so that the length of one rotation of the cholesteric structure is formed so that the liquid crystal layer reflects infrared rays with a wavelength of 900 nm. The coating film was dried to form a coating film. The coating film was irradiated with ultraviolet light or the like to harden the coating film. A liquid crystal layer containing cholesteric liquid crystals laminated on the substrate was formed.

[0045] The first surface of the liquid crystal layer of the optical film of each Example and Comparative Example was cut out to have a rectangle with a side length of 15 mm to 20 mm. A part of the cut out liquid crystal layer was fixed to a slide glass with tape. The first surface of the liquid crystal layer fixed to the slide glass was scanned with a laser microscope (VK-X150 manufactured by KEYENCE Corporation). The laser microscope was set to scan the outermost surface of the transparent body with an objective lens of 50 times and an optical zoom of 1.0 times. The scanning pitch was set to 0.13 μm so as to increase the sampling accuracy. Data was obtained by scanning the shape of the first surface of the liquid crystal layer. The data was corrected taking into consideration that the first surface of the liquid crystal layer was inclined with respect to the horizontal plane during scanning. Of the corrected data, 4096 pieces of data in the height direction with respect to the scanning direction were extracted for one direction parallel to the short side of the cut out liquid crystal layer. The extracted data was subjected to a discrete Fourier transform to obtain the power spectrum density for the spatial frequency of the concave-convex shape and the second concave-convex shape. The pitch of the discrete Fourier transform was set to 0.531 μm so that a sufficient number of data could be obtained for the spatial frequency range of 0.01 / μm to 1 / μm. Approximately four times as much data was obtained for one data point used in the discrete Fourier transform. The scanning pitch and the discrete Fourier transform pitch were set so that sufficient data suitable for the technical concept of the present invention could be obtained. The discrete Fourier transform was performed using Excel. A double logarithmic graph was plotted for the power spectrum density versus spatial frequency.

[0046] For the optical films of each Example and Comparative Example, the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm were calculated from the log-log graph of the power spectrum density versus the spatial frequency of the concave-convex shape and the second concave-convex shape. The slope of the regression line was calculated using Excel's slope function. The ratio α / β of α to β and the difference β-α between α and β were calculated.

[0047] For the optical films of each of the Examples and Comparative Examples, the arithmetic mean roughness Ra of the first surface of the liquid crystal layer was determined from data obtained by scanning the shape of the first surface of the liquid crystal layer.

[0048] The orientation of the cholesteric liquid crystal and the appearance of the optical film were evaluated for the optical films of each of the examples and comparative examples. The orientation of the cholesteric liquid crystal and the appearance of the optical film were evaluated at a total of nine locations, including both ends and three locations in the center of the long side direction of the optical film with a long side of 100 m or more, and both ends and three locations in the center of the short side direction. Regarding the orientation of the cholesteric liquid crystal, an optical film that reflected 25% or more of the infrared light with a reflection center wavelength of 900 nm irradiated to the optical film was rated as A, and an optical film that reflected less than 25% was rated as B. The light irradiated to the optical film was unpolarized. The reflectance was calculated from the total amount of reflected light, which was the sum of the regular reflection component and the diffuse reflection component. Specifically, a reflectance meter (JASCO V-670 and integrating sphere unit ISN-723) was used to irradiate the optical film with light of a specific wavelength from a direction at 45 degrees to the normal direction, and the reflectance at that wavelength was determined by expressing the ratio of the total amount of reflected light, which is the sum of the regular reflection component and the diffuse reflection component of the reflected light, to the amount of incident light, expressed as a percentage. The wavelength at which the reflectance for each wavelength of light is maximized was determined as the central reflection wavelength. Regarding the appearance of the optical film, a L * a * b * L in color space * With a black board with a value of 10 or less placed in front of it, a white spot light with an illuminance of 30 to 40 Lux was irradiated from a position 20 cm away from the front, and the appearance of the reflected light was visually observed. Optical films with no visible unevenness in the appearance were rated as A, and those with visible unevenness were rated as B.

[0049] For the optical films of each Example and Comparative Example, the α value, β value, α / β value, β-α value, Ra value, reflection center wavelength value, evaluation results of the alignment of the cholesteric liquid crystal, and evaluation results of the appearance of the optical film are shown in Table 1 below.

[0050] [Table 1]

[0051] From the comparison between the Examples and Comparative Examples, it is understood that when the value of α / β is 0.38 or more and 0.72 or less, or when the value of β-α is -0.81 or more and -0.22 or less, the cholesteric liquid crystal is appropriately aligned and the appearance of the optical film is not deteriorated. It is understood that the alignment of the cholesteric liquid crystal and the appearance of the optical film cannot be appropriately evaluated by the value of the arithmetic mean roughness Ra of the liquid crystal layer. [Explanation of symbols]

[0052] 10 Optical Film 20 Base material 21 Side 2 22 Second uneven shape 30 Liquid crystal layer 31 Page 1 32 Uneven shape 35 Cholesteric Liquid Crystal

Claims

1. A liquid crystal layer including a cholesteric liquid crystal, A concave-convex shape is formed on the first surface of the liquid crystal layer, an optical film, in which in a double logarithmic graph of power spectral density versus spatial frequency of the uneven shape, a ratio α / β of a slope α of a regression line in the spatial frequency range of 0.01 / μm to a slope β of a regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 or more and 0.72 or less.

2. A liquid crystal layer including a cholesteric liquid crystal, A concave-convex shape is formed on the first surface of the liquid crystal layer, in a double logarithmic graph of power spectral density versus spatial frequency of the concave-convex shape, a difference β-α between a slope α of a regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and a slope β of a regression line in the spatial frequency range of 0.1 / μm to 1 / μm is −0.81 or more and −0.22 or less.

3. A substrate and a liquid crystal layer laminated on a second surface of the substrate, the liquid crystal layer includes a cholesteric liquid crystal; A second uneven shape is formed on the second surface, an optical film, in which in a log-log graph of power spectral density versus spatial frequency of the second uneven shape, the ratio α / β of the slope α of the regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm to the slope β of the regression line in the spatial frequency range of 0.1 / μm to 1 / μm is 0.38 or more and 0.72 or less.

4. A substrate and a liquid crystal layer laminated on a second surface of the substrate, the liquid crystal layer includes a cholesteric liquid crystal; A second uneven shape is formed on the second surface, an optical film, in which in a log-log graph of power spectral density versus spatial frequency of the second uneven shape, a difference β-α between a slope α of a regression line in the spatial frequency range of 0.01 / μm to 0.1 / μm and a slope β of a regression line in the spatial frequency range of 0.1 / μm to 1 / μm is −0.81 or more and −0.22 or less.

5. a first surface of the liquid crystal layer facing the second surface of the base material; The optical film according to claim 3 , wherein the first surface has a concave-convex shape formed thereon to fit with the second concave-convex shape.

6. The optical film according to claim 1 , wherein the liquid crystal layer reflects circularly polarized infrared light.

Images