JP6880672B2 - Polarizing separation film - Google Patents

Description

The present invention relates to a polarizing separation film including a cholesteric liquid crystal layer.

The cholesteric liquid crystal has the property of selectively reflecting the wavelength derived from the spiral pitch of the spiral structure and also selectively reflecting the circularly polarized light in the direction derived from the turning direction in the spiral structure. Utilizing such properties of cholesteric liquid crystals, they are applied as polarizing separation films to reflective materials (Patent Document 1), projection screens (Patent Document 2), reflective polarizing plates, color compensation films and the like.

Japanese Unexamined Patent Publication No. 2016-126326 Japanese Unexamined Patent Publication No. 2005-107906

However, the conventional polarizing separation film using a cholesteric liquid crystal is viewed from the front when light is incident from an angle or when the film is viewed from an angle (when viewed from a direction having an angle with respect to the front). It may have a different color than the case.

Therefore, in view of the above problems, it is an object of the present invention to provide a polarizing separation film capable of suppressing a change in color due to a difference in viewing direction.

Hereinafter, the present invention will be described. For the sake of clarity, the reference symbols of the drawings are added in parentheses. However, the present invention is not limited to this.

One aspect of the present invention is a polarizing separation film (10) comprising a cholesteric liquid crystal layer (15) having a cholesteric liquid crystal structure having irregularities formed on at least one surface and having a diffuse reflectance of 15% or more. is there.

Another aspect of the present invention is a concavo-convex forming layer (consisting of a base material (11) and a concavo-convex-shaped layer laminated on the surface of the base material, or the surface of the base material itself is formed as concavo-convex. A polarizing separation film (10) comprising 12) and a cholesteric liquid crystal layer (15) having a cholesteric liquid crystal structure laminated on an uneven cambium, and having a diffuse reflectance of 15% or more.

According to the present invention, even if the viewing angle deviates from the front, the color change can be suppressed to be small with respect to the color viewed from the front, and light can be provided with an appropriate color even if the viewing angle is widened. ..

FIG. 1A is a perspective view of the polarizing separation film 10, and FIG. 1B is an exploded perspective view of the polarizing separation film 10. FIG. 2A is a diagram for explaining the cholesteric liquid crystal structure in the cholesteric liquid crystal layer 15 of the polarizing separation film 10, and FIG. 2B is a diagram for explaining the cholesteric liquid crystal structure of the conventional cholesteric liquid crystal layer. FIG. 3A is a plan view illustrating the form of the uneven cambium of the embodiment, and FIG. 3B is a front view thereof.

Hereinafter, the present invention will be described based on the form shown in the drawings. However, the present invention is not limited to these forms. In these drawings, even minute elements may be deformed or greatly exaggerated for the sake of clarity. Further, for the sake of readability, a part of the code may be omitted when the same element is repeatedly arranged.

1A and 1B are views for explaining one form, FIG. 1A is a perspective view of the polarizing separation film 10, and FIG. 1B is an exploded perspective view of the polarizing separation film 10. As can be seen from FIGS. 1 (a) and 1 (b), the polarizing separation film 10 of the present embodiment includes a base material 11, a concavo-convex forming layer 12, and a cholesteric liquid crystal layer 15.

The base material 11 is a transparent layer serving as a base material for laminating the uneven cambium layer 12 and the liquid crystal layer 15 on one surface thereof. As the material forming the base material 11, various materials can be used. However, a material that is widely used as a material for a member constituting an optical element, has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost can be used. This includes, for example, thermoplastic resins such as polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyether sulfones. Examples thereof include epoxy acrylate, urethane acrylate-based reactive resin (ionized radiation curable resin, etc.), triacetyl cellol roll resin, polyethylene terephthalate resin (PET), glass, and the like.
The thickness thereof can be configured in the range of 10 μm to 1000 μm.

The uneven cambium 12 is a layer that imparts unevenness to one surface of the liquid crystal layer 15, and a plurality of ridges 13 are arranged at intervals. Therefore, a convex portion 12a is formed at the portion where the convex portion 13 is arranged, a concave portion 12b is formed between the convex portions 13, and the convex portion 12a and the concave portion 12b are repeatedly formed to be uneven.
In this embodiment, the ridges 13 are columns having a semicircular cross section, and a plurality of ridges 13 are arranged along one surface of the base material 11 so that the axes of the columns are parallel.

Various materials can be used as the material forming the ridges 13 of the uneven cambium 12. However, a material that is widely used as a material for members constituting an optical element, has excellent mechanical properties, optical properties, stability, workability, and the like, and can be obtained at low cost can be used. This includes, for example, thermoplastic resins such as polymer resins having an alicyclic structure, methacrylic resins, polycarbonate resins, polystyrene resins, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, and polyether sulfones. Examples thereof include epoxy acrylate, urethane acrylate-based reactive resin (ionized radiation curable resin, etc.), triacetyl cellol roll resin, and the like.

The base material 11 and the unevenness forming layer 12 described so far may be integrated without a boundary, or may be in a form in which the unevenness forming layer 12 is laminated on the surface of the base material 11 and another member is adhered. ..
Examples of the manufacturing process include extrusion molding, molding, and photolithography. In the case of being manufactured by extrusion molding, the base material 11 and the uneven cambium 12 can be integrally formed. Further, in the case of manufacturing by shaping, the unevenness forming layer 12 can be formed by shaping on the base material 11, and in this case, the base material layer 11 and the unevenness forming layer 12 are made of the same resin. It may be a material or a different material.

In this example, as described above, the unevenness in which columnar members having a semicircular cross section are arranged is illustrated, but the present invention is not limited to this, and the cross section may be a polygon such as a triangle or a quadrangle. Further, it does not have to be columnar, and may have a form in which point-like irregularities or hemispherical irregularities are arranged along the surface of the base material 11.

The cholesteric liquid crystal layer 15 is a layer laminated on the surface of the base material 11 on the side on which the uneven cambium 12 is arranged, and is composed of a liquid crystal composition exhibiting cholesteric regularity. As the physical molecular arrangement of the liquid crystal molecules, the director of the liquid crystal molecules has a spiral structure in which the director continuously rotates in the thickness direction of the layer.

The cholesteric liquid layer layer 15 has a polarization separation property that separates a unidirectional circularly polarized light component and a unidirectional circularly polarized light component based on the physical molecular arrangement of such liquid crystal molecules. .. That is, in the cholesteric liquid crystal layer 15, the unpolarized light incident along the spiral axis is separated into two polarized light (right circularly polarized light and left circularly polarized light), one of which is transmitted and the other is reflected. To. This phenomenon is known as circular dichroism, and when the spiral winding direction in the spiral structure of the liquid crystal molecule is appropriately selected, the circularly polarized light component having the same optical rotation direction as the spiral winding direction is selectively reflected.

In addition to the reflection of the circularly polarized light component, to selectively reflect light of wavelength lambda ₀ shown by the following formula (1).
λ ₀ = _nave・ p… (1)
Here, p is the spiral pitch length in the spiral structure of the liquid crystal molecule (the length per pitch of the molecular spiral of the liquid crystal molecule), and _nave is the average refractive index in the plane orthogonal to the spiral axis.

The wavelength bandwidth Δλ of the reflected light at this time is expressed by the following equation (2). Here, Δn is a birefringence value.
△ λ ＝ △ n ・ p… (2)

That is, the unpolarized light incident on the polarizing separation film 10 belongs to the range of the wavelength bandwidth Δλ _{centered on the selective reflection center wavelength λ 0 (selective reflection wavelength range) according to the above-mentioned polarization separation characteristics.} Circularly polarized light components (for example, right-handed circularly polarized light within the selective reflection wavelength range) are reflected as reflected light, and other light (for example, left-handed circularly polarized light within the selective reflection wavelength range, right-handed circularly polarized light outside the selective reflection wavelength range) is transmitted. Will be done.

Since such a cholesteric liquid crystal layer 15 is laminated on the base material layer 11 and the concavo-convex forming layer 12, the concavo-convex forming layer 12 is formed on the surface of the cholesteric liquid crystal layer 15 on the side in contact with the concavo-convex forming layer 12. It has the opposite unevenness to the unevenness. That is, the cholesteric liquid crystal layer 15 is provided with a convex portion 15a so as to fill the concave portion 12b of the uneven cambium forming layer 12, and is provided with a concave portion 15b so as to fill the convex portion 12a of the uneven cambium forming layer 12. Therefore, in the present embodiment, the uneven cambium 12 and the cholesteric liquid crystal layer 15 have an uneven interface and are in contact with each other, so that the cholesteric liquid crystal layer 15 has an uneven surface.
On the other hand, of the cholesteric liquid crystal layer 15, the surface opposite to the uneven surface side is a smooth surface in this embodiment. However, the present invention is not limited to this, and other uneven surfaces may be formed.

By forming irregularities on at least one surface of the cholesteric liquid crystal layer 15 in this way, the liquid crystal structure of the cholesteric liquid crystal layer 15 can be configured as follows. A schematic diagram is shown in FIG. 2 (a). That is, by forming the unevenness, the spiral axis 15c shown by the dotted line is the thickness direction of the liquid crystal layer 15 (the vertical direction of the paper surface in FIG. 2A) for a part of the liquid crystal structure contained in the cholesteric liquid crystal layer 15. Can include things that are not parallel to. Due to the non-uniformity of the orientation of the spiral shaft 15c of the cholesteric liquid crystal structure, it is possible to diffuse the selectively reflected light as a whole.

Incidentally, the cholesteric liquid crystal structure of the general cholesteric liquid crystal layer 115 laminated only on the smooth base material layer 11 is in a planer-oriented state, and is included in the cholesteric liquid crystal structure as shown in FIG. 2 (b). The directions of the spiral axes shown by the dotted lines of each spiral structure extend uniformly and parallel to the thickness direction of the layer. In such a case, the selectively reflected light becomes specular reflection, and the wavelength of the selectively reflected light differs depending on the viewing angle with respect to the front surface, so that the colors look different.

The polarization separation film 10 as described above has a diffuse reflectance of 15% or more, which is the ratio of diffuse reflection to total reflection (specular reflection + diffuse reflection). As a result, it is possible to suppress the change in color depending on the viewing angle. If the diffuse reflectance is less than 15%, the color change greatly depending on the viewing angle, and it cannot be said that the effect of suppressing the color change is effective.
On the other hand, the diffuse reflectance is preferably 75% or less. This is because if the diffuse reflectance is higher than this, the haze becomes high, and the reflected color may become too white depending on the application.

The specific mode for forming the polarization separation film as described above is not particularly limited, but for example, more preferably, the haze of the base material 11 is made smaller than 88%, and Ra of the uneven cambium is formed. Can be mentioned as a form in which is configured to satisfy at least one of 0.10 μm or more and 0.49 μm or less, Rp of 0.40 μm or more and 2.09 μm or less, and Rz of 0.60 μm or more and 3.28 μm or less.
Here, Ra means the arithmetic mean roughness in JIS B 0601 (2001), Rp means the maximum mountain height in JIS B 0601 (2001), and Rz means the maximum height in JIS B 0601 (2001).

The polarizing separation film 10 as described above can be manufactured, for example, as follows. That is, it can be formed by applying a liquid crystal composition exhibiting cholesteric regularity to the base material 11 and the uneven cambium 12 and then performing an orientation treatment and a curing treatment. A more detailed example is as follows.

First, the base material 11 is prepared, and the unevenness forming layer 12 is formed on one surface of the base material 11. The method of providing the uneven cambium 12 on one surface of the base material 11 is not particularly limited, and examples thereof include etching, sandblasting, and shaping. Further, an intermediate layer such as an easy-adhesion layer may be laminated on the surface of the base material 11 on the side where the unevenness forming layer 12 is provided and on the unevenness forming layer 12 in order to improve the adhesion of the cholesteric liquid crystal layer 15. ..

Next, the cholesteric liquid crystal layer 15 is formed by applying a liquid crystal composition exhibiting cholesteric regularity on the base material 11 and the uneven cambium 12 prepared in this manner, and then performing an orientation treatment and a curing treatment. Laminate. The details are as follows.

A layer made of cholesteric liquid crystal is formed by applying a liquid crystal composition exhibiting cholesteric regularity on the base material 11 and the uneven cambium 12. At this time, any existing method can be used as the method for applying the liquid crystal composition. Specifically, a roll coating method, a gravure coating method, a bar coating method, a slide coating method, a die coating method, a slit coating method, a dipping method and the like can be used. Further, when a plastic film is used as the base material 11 and the uneven cambium, a film coating by a so-called roll-to-roll system or the like can be used.

As the liquid crystal composition to be applied, a chiral nematic liquid crystal or a cholesteric liquid crystal exhibiting cholesteric regularity can be used. Such a material is not particularly limited as long as it is a liquid crystal material capable of forming a cholesteric liquid crystal structure, but in particular, a polymerizable liquid crystal material having polymerizable functional groups at both ends of the molecule is used. It is preferable to obtain an optically stable cholesteric liquid crystal layer 15 after curing.

Here, a case where a chiral nematic liquid crystal exhibiting cholesteric regularity is used as the liquid crystal composition will be described as an example. The chiral nematic liquid crystal is a mixture of a polymerizable liquid crystal material exhibiting nematic regularity and a chiral agent. Here, the chiral agent is for controlling the spiral pitch length of the polymerizable liquid crystal material exhibiting nematic regularity so that the liquid crystal composition exhibits cholesteric regularity as a whole. Further, a polymerization initiator and an additive are appropriately added to such a liquid crystal composition.

Examples of the polymerizable liquid crystal material exhibiting nematic regularity include compounds represented by the following general formula (1) and compounds represented by the following formulas (2-i) to (2-xi). Can be mentioned. Moreover, these compounds can be used alone or in mixture.

In the above formula (1), R ¹ and R ² each represent a hydrogen or a methyl group, but it is preferable that both ^{R 1} and R ^{2 are hydrogen because of the wide temperature range indicating the liquid crystal phase.} X in the formula (1) may be hydrogen, chlorine, bromine, iodine, an alkyl group having 1 to 4 carbon atoms, a methoxy group, a cyano group, or a nitro group, but may be a chlorine or a methyl group. preferable. Further, in the above formula (1), a and b indicating the chain lengths of the (meth) acryloyloxy groups at both ends of the molecular chain and the alkylene group which is a spacer between the aromatic rings are individually arbitrary integers in the range of 2 to 12, respectively. However, it is preferably in the range of 4 to 10, and more preferably in the range of 6 to 9. The compound of the formula (1) having a = b = 0 has poor stability, is susceptible to hydrolysis, and has high crystallinity of the compound itself. Further, the compound of the general formula (1) in which a and b are 13 or more, respectively, has a low isotropic transition temperature (TI). For this reason, both of these compounds have a narrow temperature range showing the liquid crystal phase, which is not preferable.

In the above, examples of polymerizable liquid crystal monomers have been given as examples of polymerizable liquid crystal materials exhibiting nematic regularity, but the present invention is not limited to this, and polymerizable liquid crystal oligomers, polymerizable liquid crystal polymers, liquid crystal polymers, etc. are used. It can also be used. As such a polymerizable liquid crystal oligomer, a polymerizable liquid crystal polymer, or a liquid crystal polymer, it can be appropriately selected and used from those conventionally proposed.

On the other hand, the chiral agent is a low molecular weight compound having an optically active site, and is mainly a compound having a molecular weight of 1500 or less. Chiral agents are mainly used for the purpose of inducing a helical structure in the positive uniaxial nematic regularity expressed by a polymerizable liquid crystal material exhibiting nematic regularity. As long as this purpose is achieved, it will be compatible with the polymerizable liquid crystal material exhibiting nematic regularity in a solution state or in a molten state without impairing the liquid crystal property of the polymerizable liquid crystal material exhibiting nematic regularity. The type of low molecular weight compound as a chiral agent is not particularly limited as long as it can induce a desired spiral structure.

The chiral agent used to induce a spiral structure in the liquid crystal in this way needs to have at least some chirality in the molecule. Therefore, examples of the chiral agent used here include compounds having one or more asymmetric carbons, compounds having asymmetric points on heteroatoms such as chiral amines and chiral sulfoxides, or cumlenes. Examples thereof include compounds having an optically active site having an axial asymmetry such as and binaphthol. More specifically, a commercially available chiral nematic liquid crystal (for example, chiral dopant liquid crystal S-811 (manufactured by Merck)) can be mentioned.

However, depending on the properties of the chiral agent selected, the nematic regularity formed by the polymerizable liquid crystal material exhibiting nematic regularity is disrupted, the orientation is reduced, or the liquid crystallinity is formed when the chiral agent is non-polymerizable. There is a risk that the curability of the composition will decrease and the reliability of the film after curing will decrease. Further, the use of a large amount of the chiral agent having an optically active site leads to an increase in the cost of the liquid crystal composition. Therefore, when forming a liquid crystal layer having a cholesteric regularity with a short spiral pitch length, as a chiral agent having an optically active moiety contained in the liquid crystal composition, a chiral agent having a large effect of inducing a spiral structure is used. It is preferable to select, and specifically, it is preferable to use a low molecular weight compound having an axial asymmetry in the molecule as represented by the following formula (3), (4) or (5).

In the above formula (3) or formula (4), R ⁴ represents a hydrogen or methyl group. Y is any one of the formulas (i) to (xxiv) shown above, and among them, any one of the formulas (i), (ii), (iii), (v) and (vii). Is preferable. Further, c and d indicating the chain length of the alkylene group can individually take any integer in the range of 2 to 12, but preferably in the range of 4 to 10, and preferably in the range of 6 to 9. Is even more preferable. The compound of the above formula (3) or (4) having a value of c or d of 0 or 1 lacks stability, is susceptible to hydrolysis, and has high crystallinity. On the other hand, a compound having a c or d value of 13 or more has a low melting point (Tm). In these compounds, the compatibility with the polymerizable liquid crystal material exhibiting nematic regularity is lowered, and phase separation or the like may occur depending on the concentration.

It should be noted that such a chiral agent does not need to be particularly polymerizable. However, when the chiral agent has polymerizability, it is polymerized with a polymerizable liquid crystal material exhibiting nematic regularity, and the cholesteric regularity is stably immobilized. Therefore, in terms of thermal stability and the like. preferable. In particular, it is preferable that both ends of the molecule have polymerizable functional groups in order to obtain the cholesteric liquid crystal layer 15 having good heat resistance.

The optimum amount of the chiral agent contained in the liquid crystal composition is determined in consideration of the ability to induce a spiral structure, the cholesteric liquid crystal structure of the cholesteric liquid crystal layer 15 finally obtained, and the like.

The liquid crystal composition can be applied as it is on the base material 11 and the uneven cambium 12, but an appropriate solvent such as an organic solvent is used for the purpose of adjusting the viscosity to the coating device and obtaining a good orientation state. It may be dissolved in a solvent to form an ink.

After the liquid crystal composition is applied onto the base material 11 and the uneven cambium 12 to form the cholesteric liquid crystal layer as described above, the cholesteric liquid crystal layer is held at a predetermined temperature at which the cholesteric liquid crystal structure is developed, and the cholesteric liquid crystal layer is formed. Orient the liquid crystal molecules inside.

The cholesteric liquid crystal structure of the cholesteric liquid crystal layer 15 to be finally obtained in this example is not in the planer orientation state, but the direction of the spiral axis of the cholesteric liquid crystal varies in the layer as shown in FIG. 2 (a). It is in an oriented state. However, even in this case, the orientation treatment is required. That is, the orientation treatment for aligning the directors of the liquid crystal molecules of the cholesteric liquid crystal structure in a certain direction on the base material 11 is not required, but the orientation treatment for forming a plurality of spiral structures in the cholesteric liquid crystal structure is necessary. Because it becomes.

Here, when the laminated cholesteric liquid crystal layer is held at a predetermined temperature at which the cholesteric liquid crystal structure is expressed, the cholesteric liquid crystal layer exhibits a liquid crystal phase, and the director of the liquid crystal molecules becomes a layer due to the self-integration action of the liquid crystal molecules themselves. A spiral structure formed by continuously rotating in the thickness direction is formed. The cholesteric liquid crystal structure expressed in such a liquid crystal phase state can be immobilized by curing the cholesteric liquid crystal layer by a method as described later.

When the applied liquid crystal composition contains a solvent, such an orientation treatment is usually performed together with a drying treatment for removing the solvent. In addition, in order to remove the solvent, it is carried out at a predetermined drying temperature, and the drying time (heating time) is appropriately set to the time during which the cholesteric liquid crystal structure is developed and the solvent is substantially removed.

After orienting the liquid crystal molecules in the cholesteric liquid crystal layer as described above, the cholesteric liquid crystal layer is cured to immobilize the cholesteric liquid crystal structure expressed in the state of the liquid crystal phase.

Here, as a method of hardening treatment,
(1) Method of drying the solvent in the liquid crystal composition (2) Method of polymerizing liquid crystal molecules in the liquid crystal composition by heating (3) Liquid crystal by irradiation with ionizing radiation (including electron beam and ultraviolet rays) A method of polymerizing liquid crystal molecules in the composition (4) A method of combining at least two of the above (1) to (3) can be mentioned.

By performing each of the above steps, the polarizing separation film 10 having the cholesteric liquid crystal layer 15 can be manufactured.

According to the polarizing separation film 10 described so far, the cholesteric liquid crystal layer 15 selectively reflects light having a specific wavelength and a polarizing component based on the cholesteric liquid crystal structure provided therein, and transmits other light. To do. Therefore, it can be applied to various devices that utilize this property. Applications include, for example, in display devices such as liquid crystal displays, films that improve brightness, color filters, and the like. In addition, it can be applied to a wide range of fields such as an infrared reflective film.

Further, since the unevenness is formed on at least one surface of the cholesteric liquid crystal layer 15, the spiral axis direction of the cholesteric liquid crystal structure becomes non-uniform, and diffuse reflection occurs. Since the diffuse reflection has a diffuse reflectance of 15% or more, it is possible to suppress the color change even if the viewing angle with respect to the front is changed. This makes it possible to prevent the problem of color change from occurring even when the viewing angle is widened.

Although the above-mentioned polarizing separation film 10 includes the base material layer 11 and the uneven cambium layer 12, it is sufficient that the convexity is formed on at least one of the cholesteric liquid crystal layers. Therefore, as long as the cholesteric liquid crystal layer has irregularities, the polarizing separation film of the present invention can be obtained even if the substrate layer 11 and the uneven cambium are not provided.

In the example, a plurality of polarizing separation films having various irregularities formed on the cholesteric liquid crystal layer were prepared, and the change in color depending on the diffuse reflectance and the viewing angle of each polarizing separation film was confirmed.

[Polarizing separation film]
No. As No. 1, according to the example described above, a concavo-convex forming layer also made of PET is provided on one surface of a smooth base material made of PET, and a cholesteric liquid crystal is laminated therein, and the diffuse reflectance is 16.7%. A polarizing separation film was prepared.
No. As No. 2, No. A polarizing separation film having a diffuse reflectance of 38.1% was produced by changing the form of the unevenness of the uneven cambium of No. 1.
No. As No. 3, unevenness was formed on one surface of the base material made of PET to form an unevenness forming layer, and a cholesteric liquid crystal was laminated therein to prepare a polarizing separation film having a diffuse reflectance of 63.3%.
No. As No. 4, No. A polarizing separation film having a diffuse reflectance of 71.7% was produced by changing the form of the uneven cambium of No. 3.
No. As No. 5, a cholesteric liquid crystal was laminated on one surface of a PET substrate having smooth surfaces on both sides to prepare a polarizing separation film having a diffuse reflectance of 9.0%.
No. As No. 6, both sides are smooth and the above No. 1-No. A cholesteric liquid crystal was laminated on one surface of a PET base material of a type different from that of No. 5 to prepare a polarizing separation film having a diffuse reflectance of 13.7%.

No. 1-No. The cholesteric liquid crystal used in each of the examples 6 was PALIOCOLOR manufactured by BASF Japan Ltd., and was formed so that the layer thickness was in the range of 0.5 μm to 1.0 μm at any place.

In addition, No. 1-No. As shown in FIGS. 3 (a) and 3 (b), the hemispherical protrusions 20 are two-dimensionally vertically and horizontally (matrix-like) along the surface of the base material in each of the morphologies of the uneven cambium in the fourth example. It is arranged alternately (staggered) so that the rows and columns are staggered by half a pitch. Then, the roughness Ra was changed for each example. Ra of each example is shown in Table 1 with the results. As shown in Table 1, No. 2 is at least No. Ra was larger than 1.

The diffuse reflectance (%) of each polarizing separation film is a value obtained by expressing the ratio of the diffuse reflection light to the total reflected light by the polarizing separation film as a percentage, and more specifically,
(Diffuse reflected light / (Specular reflected light + Diffuse reflected light)) x 100%
Is required by.

Diffuse reflected light and specularly reflected light can be obtained as follows.
A polarizing separation film is placed on the integrating sphere, and the polarizing separation film is irradiated with light from a direction of 45 degrees with respect to the normal direction of the polarizing separation film. Then, the specular reflection component is excluded from the integrating sphere from the light reflected by the polarizing separation film with respect to the irradiation light, and this is measured and used as the specular reflection light. On the other hand, the other reflected light diffusely reflected in the integrating sphere is summed up to obtain diffuse reflected light.

[Evaluation]
The color change suppressing effect was evaluated for each of the above polarizing separation films. Specifically, it is as follows.

<Color change suppression effect>
The effect of suppressing color change was confirmed by the following two methods (A) and (B), and the one that was effective in both was "○", and the one that was particularly effective was "◎". On the other hand, those that showed an effect were marked with "Δ", and those that did not show any effect were marked with "x".
Method (A): The reflectance is measured for each incident light angle (5 °, 30 °, 60 ° with respect to the front) using a reflectance measuring device (Nippon Kogaku Co., Ltd., V-600), and this reflection is measured. After converting the rate to chromaticity, the effect is confirmed by the magnitude of the change in chromaticity coordinates for each measurement angle.
Method (B): Visual confirmation of appearance. Check the color when viewed from an angle of 30 ° with respect to the front of the polarizing separation film, and judge whether there is a color change.

[result]
Table 1 shows the diffuse reflectance and the evaluation results (color change suppression).

As can be seen from the results in Table 1, by setting the diffuse reflectance to 15% or more, it is possible to suppress the occurrence of color change even when viewed from a direction having an angle with respect to the front surface. Further, by setting the diffuse reflectance to 38% or more, the effect becomes more remarkable.

10 Polarizing separation film 11 Base material 12 Concavo-convex forming layer 13 Convex 15 Cholesteric liquid crystal layer

Claims (2)

A cholesteric liquid crystal layer having a cholesteric liquid crystal structure having irregularities formed on at least one surface thereof is provided.
The unevenness is an unevenness formed by arranging a plurality of columnar recesses having a semicircular cross section at intervals.
A polarizing separation film having a diffuse reflectance of 15% or more. With the base material
A concavo-convex cambium composed of a concavo-convex layer laminated on the surface of the base material, or the surface of the base material itself being formed concavo-convex.
A cholesteric liquid crystal layer having a cholesteric liquid crystal structure laminated on the uneven cambium is provided.
The unevenness of the unevenness-forming layer is an unevenness formed by arranging a plurality of columnar convex portions having a semicircular cross section at intervals.
Diffuse reflectance is 15% or more,
Polarizing separation film.

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