Polymer-dispersed liquid crystal film

Abstract

The present invention provides a polymer-dispersed liquid crystal film comprising a first transparent conductive film, a polymer-dispersed liquid crystal layer, and a second transparent conductive film in this order, wherein the polymer-dispersed liquid crystal layer includes a polymer matrix and droplets which are dispersed in the polymer matrix and which contain a liquid crystal component and a dichroic dye, and the average oblateness of the droplets is not less than 0.3.

Description

Polymer dispersed liquid crystal film

[0001] The present invention relates to a polymer dispersed liquid crystal film.

[0002] A PDLC film having a polymer dispersed liquid crystal (hereinafter, sometimes referred to as "PDLC") layer containing a polymer matrix and liquid crystal droplets between a pair of transparent electrode layers can change the degree of scattering of transmitted light in the PDLC layer depending on the amount of applied voltage. For example, a PDLC film can be switched between a light transmitting state (transparent state) and a light scattering state (scattering state) by switching between a voltage applied state and a voltage not applied state (Patent Document 1).

[0003] In the above-mentioned PDLC film, when a dichroic dye is contained in the liquid crystal component droplets, by switching between a voltage application state and a voltage non-application state, it is possible to switch between a state in which light absorption by the dichroic dye is suppressed (non-colored state) and a state in which light absorption by the dichroic dye occurs (colored state) (Patent Document 2). Such PDLC films are being increasingly applied as light-control films useful for privacy protection, information security, energy conservation, etc. to windows, walls, partitions, etc. in vehicles such as cars and trains, offices, commercial facilities, residences, etc.

[0004] JP 2002-189123 A International Publication No. 2022 / 186062

[0005] Conventional PDLC films using dichroic dyes may have insufficient light-shielding properties in applications where light-shielding properties are required, and therefore there is a demand for improved light-shielding properties of PDLC films in a colored state (in other words, reduced light leakage).

[0006] The present invention has been made to solve the above problems, and its main object is to provide a PDLC film that can be switched between a colored state and a non-colored state and has improved light-blocking properties in the colored state. In addition, it is generally preferable that the operating voltage of the PDLC film is low.

[0007] [1] According to one aspect of the present invention, there is provided a polymer-dispersed liquid crystal film comprising, in this order, a first transparent conductive film, a polymer-dispersed liquid crystal layer, and a second transparent conductive film, wherein the polymer-dispersed liquid crystal layer comprises a polymer matrix and droplets dispersed in the polymer matrix, the droplets containing a liquid crystal component and a dichroic dye, the droplets having an average flatness of 0.3 or more. [2] In the polymer-dispersed liquid crystal film described in [1] above, the average particle diameter of the droplets in a cross section perpendicular to the main surface may be 0.1 μm or more and 10 μm or less. [3] In the polymer-dispersed liquid crystal film described in [1] or [2] above, the content of the dichroic dye in the polymer-dispersed liquid crystal layer may be 0.5 wt % or more. [4] In the polymer-dispersed liquid crystal film described in any one of [1] to [3] above, the thickness of the polymer-dispersed liquid crystal layer may be 30 μm or less. [5] The polymer dispersed liquid crystal film according to any one of [1] to [4] above may have a total light transmittance of 20% or less when no voltage is applied. [6] The polymer dispersed liquid crystal film according to any one of [1] to [5] above may have a total light transmittance of 20% or more when a voltage is applied. [7] The polymer dispersed liquid crystal film according to any one of [1] to [6] above may have a haze of 20% or less when a voltage is applied.

[0008] According to an embodiment of the present invention, the droplets of the liquid crystal component containing the dichroic dye are flat in the thickness direction, so that light leakage is less likely to occur even when the PDLC layer is thin. As a result, a PDLC film can be obtained that can switch between a colored state and a non-colored state at an appropriate operating voltage and has improved light-blocking properties in the colored state.

[0009] 1 is a schematic diagram for explaining a method for reducing light leakage in a PDLC film using a dichroic dye. 2 is a schematic diagram for explaining the configuration of a PDLC film in a voltage-applied state according to one embodiment of the present invention. 3 is a schematic diagram for explaining the configuration of a PDLC film in a voltage-unapplied state according to one embodiment of the present invention. 4 is a schematic diagram for explaining a method for measuring the oblateness of a liquid crystal droplet.

[0010] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and are not intended to limit the interpretation of the present invention. In this specification, the term "to" indicating a range of values ​​includes the upper and lower limits.

[0011] A. Polymer-Dispersed Liquid Crystal (PDLC) Film A PDLC film according to an embodiment of the present invention includes, in this order, a first transparent conductive film, a PDLC layer, and a second transparent conductive film, the PDLC layer including a polymer matrix and droplets (hereinafter sometimes referred to as "liquid crystal droplets") dispersed in the polymer matrix and containing a liquid crystal component and a dichroic dye. The liquid crystal droplets in the PDLC layer have an average flatness of, for example, 0.3 or more.

[0012] In PDLC films using dichroic dyes, a small PDLC layer thickness is preferable from the viewpoint of reducing operating voltage. However, reducing the thickness of the PDLC layer tends to increase light leakage. Here, as shown in FIG. 1( a), reducing the thickness of the PDLC layer 20 and increasing the concentration of dichroic dye in the liquid crystal droplets 25 can be considered to reduce light leakage. However, when the thickness of the PDLC layer 20 is small, light leakage may occur in areas where the amount of liquid crystal droplets 25 present in the thickness direction (more specifically, the amount of dichroic dye present) is insufficient. To address this issue, as shown in FIG. 1( b), reducing the particle size of the liquid crystal droplets 25 and improving the uniformity of their dispersion can be considered to reduce light leakage. However, this method has the problem of increasing the operating voltage. In contrast, in PDLC films according to embodiments of the present invention, as shown in FIG. 1( c), the liquid crystal droplets 25 are flat, allowing a sufficient amount of liquid crystal droplets 25 (more specifically, dichroic dye) to be present in the thickness direction even when the PDLC layer 20 is thin. This makes it possible to effectively suppress light leakage in a thin PDLC layer, resulting in a PDLC film that can be switched between a colored state and a non-colored state at an appropriate operating voltage and has improved light-blocking properties in the colored state.

[0013] As described above, the appearance of the PDLC film changes depending on the applied voltage. In one embodiment, the PDLC film is in a non-colored state when a voltage is applied and in a colored state when no voltage is applied (normal mode). In another embodiment, the PDLC film is in a colored state when a voltage is applied and in a non-colored state when no voltage is applied (reverse mode). Here, the "non-colored state" does not mean a completely colorless state, as long as the dichroic dye absorbs less light than in the "colored state."

[0014] 2 and 3 are schematic cross-sectional views illustrating the configuration of an example of a normal-mode PDLC film according to an embodiment of the present invention. FIG. 2 illustrates a state in which a voltage (electric field) is applied to the PDLC layer (non-colored state), and FIG. 3 illustrates a state in which a voltage (electric field) is not applied to the PDLC layer (colored state). The PDLC film 100 includes, in this order, a first transparent conductive film 10, a PDLC layer 20 including a polymer matrix 22 and liquid crystal droplets 25 dispersed in the polymer matrix 22, and a second transparent conductive film 30. The liquid crystal droplets 25 are so-called guest-host liquid crystal droplets including a liquid crystal component 23 and a dichroic dye 24. As shown in FIG. 2, when a voltage is applied, the liquid crystal component 23 is oriented along the electric field direction (thickness direction in the illustrated example), and the dichroic dye 24 is also oriented along the liquid crystal component 23. This suppresses light absorption by the dichroic dye 24, resulting in the PDLC film 100 being in a non-colored state. Furthermore, as a result of the decrease in the difference between the refractive index of the liquid crystal droplets 25 and that of the polymer matrix 22, the PDLC film 100 exhibits a low haze. Meanwhile, as shown in Figure 3, when no voltage is applied, the degree of orientation in the thickness direction of the liquid crystal component 23 and dichroic dye 24 in the liquid crystal droplets 25 decreases (in the illustrated example, the directors of the liquid crystal component and dichroic dye are distributed in-plane). This causes the dichroic dye 24 to absorb at least some wavelengths of light, resulting in a colored PDLC film 100. Furthermore, as a result of the increase in the difference between the refractive index of the liquid crystal droplets 25 and that of the polymer matrix 22, the PDLC film 100 exhibits a high haze.

[0015] Although not shown, in a reverse-mode PDLC film, an alignment film is provided on the PDLC layer side surface of the transparent conductive film, so that when no voltage is applied, the liquid crystal component 23 and dichroic dye 24 in the liquid crystal droplets 25 are aligned in the thickness direction, resulting in a non-colored state, and when a voltage is applied, the alignment state of the liquid crystal component 23 and dichroic dye 24 is changed, resulting in a colored state.

[0016] The total light transmittance of a PDLC film in a colored state is typically lower than that of a PDLC film in an uncolored state. The total light transmittance of a PDLC film in a colored state may be, for example, 20% or less, 10% or less, 5% or less, or 3% or less, and may be, for example, 0.1% or more, or 0.3% or more. The total light transmittance of a PDLC film in an uncolored state may be, for example, 20% or more, 25% or more, or 30% or more, and may be, for example, 70% or less, or 60% or less. The difference in total light transmittance between the colored and uncolored states of the PDLC film may be, for example, 10% or more, 20% or more, or 30% or more. The total light transmittance can be measured in accordance with JIS K 7361. For example, the total light transmittance can be measured using a haze meter (manufactured by Nippon Denshoku Co., Ltd., product name "NDH4000").

[0017] The haze of a PDLC film in a colored state is typically higher than the haze of a PDLC film in an uncolored state. The haze of a PDLC film in a colored state may be, for example, 60% or more, 70% or more, or 80% or more, or, for example, 100% or less, 99.9% or less, or 99.8% or less. The haze of a PDLC film in an uncolored state may be, for example, 20% or less, 15% or less, or 10% or less, or, for example, 0.5% or more, 1% or more, or 2% or more. The difference in haze between the colored and uncolored states of a PDLC film may be, for example, 10% or more, 20% or more, 30% or more, or 40% or more. Haze can be measured according to JIS K 7136. For example, haze can be measured using a haze meter (manufactured by Nippon Denshoku Co., Ltd., product name "NDH4000").

[0018] The voltage applied to the PDLC film during voltage application is a voltage capable of operating the PDLC film (operating voltage), and may be, for example, 5 V to 200 V, and preferably 10 V to 150 V. In this specification, "when a voltage is applied" or "voltage applied state" refers to a state in which an operating voltage is applied to the PDLC film, and may be, for example, a state in which a voltage of 100 V is applied.

[0019] The total thickness of the PDLC film is, for example, 30 μm to 250 μm, preferably 50 μm to 150 μm.

[0020] A-1. First Transparent Conductive Film The first transparent conductive film 10 typically includes a first transparent substrate 12 and a first transparent electrode layer 14 provided on one side thereof (the PDLC layer 20 side). The first transparent conductive film 10 may optionally include a hard coat layer on one or both sides of the first transparent substrate 12, and may also include a refractive index adjusting layer between the first transparent substrate 12 and the first transparent electrode layer 14.

[0021] The surface resistance value of the first transparent conductive film is preferably 1 Ω / □ to 1000 Ω / □, more preferably 5 Ω / □ to 300 Ω / □, and even more preferably 10 Ω / □ to 200 Ω / □.

[0022] The haze value of the first transparent conductive film is preferably 20% or less, more preferably 10% or less, and even more preferably 0.1% to 10%.

[0023] The total light transmittance of the first transparent conductive film is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more.

[0024] The first transparent substrate can be formed using any appropriate material. Typically, the first transparent substrate is a polymer film mainly composed of a thermoplastic resin. Examples of thermoplastic resins include polyester-based resins; cycloolefin-based resins such as polynorbornene; acrylic resins; polycarbonate-based resins; and cellulose-based resins. Of these, polyester-based resins, cycloolefin-based resins, and acrylic resins are preferred. These resins are excellent in transparency, mechanical strength, thermal stability, moisture-blocking properties, and the like. The above thermoplastic resins may be used alone or in combination of two or more.

[0025] The thickness of the first transparent substrate is preferably 200 μm or less, more preferably 3 μm to 100 μm, and even more preferably 5 μm to 70 μm. By setting the thickness of the first transparent substrate to 200 μm or less, the function of the PDLC layer can be fully exhibited.

[0026] The total light transmittance of the first transparent substrate is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more.

[0027] The first transparent electrode layer may be made of, for example, indium tin oxide (ITO), zinc oxide (ZnO), or tin oxide (SnO ２ The first transparent electrode layer may be formed using a metal oxide such as ZnO. In this case, the metal oxide may be an amorphous metal oxide or a crystallized metal oxide. The first transparent electrode layer may also be formed using metal nanowires such as silver nanowires (AgNW), carbon nanotubes (CNT), an organic conductive film, a metal layer, or a laminate thereof. Preferably, a transparent electrode layer containing ITO is formed. A transparent electrode layer containing ITO has excellent transparency. The first transparent electrode layer may be patterned into a desired shape depending on the purpose.

[0028] The total light transmittance of the first transparent electrode layer is preferably 85% or more, more preferably 87% or more, and even more preferably 90% or more. By using a transparent electrode layer having a total light transmittance in this range, a PDLC film having a high total light transmittance in an uncolored state can be obtained. The higher the total light transmittance, the more preferable it is, and the upper limit is, for example, 99%.

[0029] The thickness of the first transparent electrode layer is, for example, 10 nm or more, preferably 15 nm or more, and for example, 50 nm or less, preferably 35 nm or less, more preferably 30 nm or less.

[0030] The first transparent electrode layer is formed on one surface of the first transparent substrate by, for example, sputtering. After forming the metal oxide layer by sputtering, it can be crystallized by annealing. Annealing is performed by, for example, heat treatment at 120°C to 300°C for 10 to 120 minutes.

[0031] The refractive index adjusting layer and the hard coat layer may have a structure well known in the art, and therefore detailed description of their structures will be omitted.

[0032] A-2. Polymer-Dispersed Liquid Crystal Layer The PDLC layer 20 includes a polymer matrix 22 and liquid crystal droplets 25 dispersed in the polymer matrix 22. The liquid crystal droplets 25 include a liquid crystal component 23 and a dichroic dye 24. As described above, the average flatness of the liquid crystal droplets in the PDLC layer is, for example, 0.3 or more, preferably 0.4 or more, and more preferably 0.5 or more. By flattening the liquid crystal droplets in the thickness direction, light leakage through the PDLC film in a colored state can be suitably suppressed. The average flatness can be, for example, 0.9 or less, or, for example, 0.8 or less.

[0033] The average flatness of the liquid crystal droplets can be determined by the following method: (1) A microscopic image of a cross section perpendicular to the main surface of the PDLC layer is obtained, and for each of 50 liquid crystal droplets randomly selected from the image, the flatness ((a-b) / a) is determined, where a is the diameter in the in-plane direction (X direction) and b is the diameter in the thickness direction (Z direction), and the average value Ave ｘ (2) Microscopic images of the main surface of the PDLC layer and a cross section perpendicular to the cross section of (1) above are obtained, and for each of 50 liquid crystal droplets randomly selected from the image, the oblateness ((a-b) / a) is calculated, where a is the diameter in the in-plane direction (Y direction) and b is the diameter in the thickness direction (Z direction), and the average value Ave ｙ (3) Calculate the average value Ave of the above two values. ｘ , Ave ｙThe smaller of these values ​​is adopted as the average flattening of the liquid crystal droplet. In (1) and (2) above, the diameter a in the in-plane direction and the diameter b in the thickness direction of the liquid crystal droplet are respectively the lengths of the sides parallel to the in-plane direction and the thickness direction of the circumscribed rectangle of the liquid crystal droplet 25, the four sides of which are parallel to the in-plane direction (X or Y direction) or the thickness direction (Z direction) in the microscope observation image I (see FIG. 4). The X direction may be any direction in a plane parallel to the main surface of the PDLC layer, for example, it may be a direction parallel to the stretching direction in the PDLC film production method described below.

[0034] In one embodiment, the ratio of the two average values ​​(Ave ｘ / Ave ｙ ) is between 1 / 2 and 2 / 1, and may be between 2 / 3 and 3 / 2, or between 3 / 4 and 4 / 3. ｘ / Ave ｙ ) is within the above range, the effects of the present invention can be more suitably obtained.

[0035] The average particle diameter of the liquid crystal droplets is, for example, 0.01 μm to 30 μm, preferably 0.05 μm to 20 μm, and more preferably 0.1 μm to 10 μm. The average particle diameter of the liquid crystal droplets is the volume-average particle diameter of the liquid crystal droplets in a cross section perpendicular to the main surface of the PDLC film, and can be determined, for example, by the following method. <Method for Measuring the Average Particle Diameter of Liquid Crystal Droplets> The PDLC film is sliced ​​perpendicular to the main surface in a cooled environment, and the vertical cross section of the exposed PDLC layer is smoothed using a microtome. Next, the vertical cross section of the PDLC layer is observed with a scanning electron microscope (SEM) to obtain a cross-sectional SEM image. The area-equivalent circle diameter (Heywood diameter) is calculated from the cross-sectional area of ​​all liquid crystal droplets in a 30 μm × 20 μm region in the cross-sectional SEM image, and the volume-average particle diameter (median diameter) is calculated by taking statistics weighted by the volume estimated as a sphere for each equivalent diameter.

[0036] The polymer matrix may be composed of any appropriate resin. The resin for forming the polymer matrix may be appropriately selected depending on the light transmittance, the refractive index of the liquid crystal component, the adhesion to the transparent conductive film, the stretchability, etc. The resin for forming the polymer matrix preferably has a refractive index similar to that of the liquid crystal component.

[0037] Specific examples of the polymer matrix-forming resin include thermoplastic resins such as urethane resins, polyvinyl alcohol resins, polyethylene resins, polypropylene resins, and acrylic resins. These are preferably water-soluble or water-dispersible resins. Only one type of polymer matrix-forming resin may be used, or two or more types may be used in combination.

[0038] The liquid crystal component may be any suitable liquid crystal compound, either singly or in combination. The birefringence of the liquid crystal component at a wavelength of 589 nm (Δn=refractive index in the long axis direction of the liquid crystal component, no=refractive index in the short axis direction of the liquid crystal component) is preferably 0.05 to 0.50, more preferably 0.10 to 0.45.

[0039] The liquid crystal component may have a positive or negative dielectric anisotropy. The liquid crystal component may be, for example, a nematic liquid crystal, a smectic liquid crystal, or a cholesteric liquid crystal. Nematic liquid crystals are preferred because they have excellent transparency in the uncolored state.

[0040] Examples of nematic liquid crystal compounds include biphenyl-based compounds, phenylbenzoate-based compounds, cyclohexylbenzene-based compounds, azoxybenzene-based compounds, azobenzene-based compounds, azomethine-based compounds, terphenyl-based compounds, biphenylbenzoate-based compounds, cyclohexylbiphenyl-based compounds, phenylpyridine-based compounds, cyclohexylpyrimidine-based compounds, cholesterol-based compounds, and fluorine-based compounds.

[0041] As the dichroic dye, any appropriate dichroic dye that is compatible with the liquid crystal component can be used. The dichroic dye may have a positive Δε or a negative Δε. The dichroic dye itself may exhibit liquid crystallinity. The dichroic dye may be used alone or in combination of two or more.

[0042] Specific examples of dichroic dyes include azo dyes, anthraquinone dyes, naphthoquinone dyes, perylene dyes, quinophthalone dyes, tetrazine dyes, and benzothiadiazole dyes. Among these, from the viewpoints of absorption coefficient, solubility in liquid crystal components, light resistance, and the like, it is preferable that the dichroic dye contains an anthraquinone dye or an azo dye. For example, the azo dyes, anthraquinone dyes, or mixtures thereof described in "Liquid Crystal Device Handbook," edited by Committee 142 of the Japan Society for the Promotion of Science, published by the Japan Industrial Newspaper Co., Ltd. (1989), pages 192 to 196 and 724 to 730, can be used. Various dichroic dyes are commercially available, and these can be used as appropriate.

[0043] The content of the liquid crystal component in the PDLC layer is, for example, 30 to 90% by weight, preferably 35 to 85% by weight, and more preferably 40 to 80% by weight.

[0044] The content of the dichroic dye in the PDLC layer is, for example, 0.05 to 13% by weight, preferably 0.5 to 10% by weight, and may be 1% by weight or more, or 3% by weight or more, and may be 6% by weight or less. The content of the dichroic dye in the PDLC layer is, for example, 0.1 to 20 parts by weight, preferably 1 to 15 parts by weight, and more preferably 3 to 10 parts by weight, per 100 parts by weight of the liquid crystal component.

[0045] The weight ratio (former:latter) of the content of the polymer matrix to the total content of the liquid crystal component and the dichroic dye in the PDLC layer is, for example, 10:90 to 70:30, preferably 15:85 to 65:35, and more preferably 20:80 to 60:40.

[0046] The total content of the polymer matrix, liquid crystal component, and dichroic dye in the PDLC layer is, for example, 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more, and is, for example, 100% by weight or less, preferably 99% by weight or less.

[0047] The PDLC layer may further contain any appropriate component, if necessary, such as a dispersing agent, a leveling agent, a crosslinking agent, etc.

[0048] Examples of the dispersant include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. The content of the dispersant in the PDLC layer is preferably 0.5% by weight to 15% by weight, and more preferably 1% by weight to 10% by weight.

[0049] Examples of the leveling agent include an acrylic leveling agent, a fluorine-based leveling agent, a silicone-based leveling agent, etc. The content of the leveling agent in the PDLC layer is preferably 0.1% by weight to 10% by weight, and more preferably 0.5% by weight to 5% by weight.

[0050] Examples of the crosslinking agent include an aziridine-based crosslinking agent, an isocyanate-based crosslinking agent, etc. The content of the crosslinking agent in the PDLC layer is preferably 0.5% by weight to 20% by weight, and more preferably 1% by weight to 10% by weight.

[0051] The thickness of the PDLC layer is, for example, 50 μm or less, preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less, and may be, for example, 1 μm or more, 3 μm or more, or 5 μm or more. When the thickness of the PDLC layer is within the above range, a PDLC film having a low operating voltage and excellent shielding properties can be suitably obtained.

[0052] A-3. Second Transparent Conductive Film The second transparent conductive film 30 typically includes a second transparent substrate 32 and a second transparent electrode layer 34 provided on one side thereof (the PDLC layer 20 side). The second transparent conductive film 30 may optionally include a hard coat layer on one or both sides of the second transparent substrate 32, and may also include a refractive index adjusting layer between the second transparent substrate 32 and the second transparent electrode layer 34.

[0053] The surface resistance value of the second transparent conductive film is preferably 1 Ω / □ to 1000 Ω / □, more preferably 5 Ω / □ to 300 Ω / □, and even more preferably 10 Ω / □ to 200 Ω / □.

[0054] The haze value of the second transparent conductive film is preferably 20% or less, more preferably 10% or less, and even more preferably 0.1% to 10%.

[0055] The total light transmittance of the second transparent conductive film is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more.

[0056] The second transparent substrate and the second transparent electrode layer can be described in the same manner as the first transparent substrate and the first transparent electrode layer, respectively. The second transparent conductive film may have the same configuration as the first transparent conductive film, or may have a different configuration.

[0057] B. Method for Manufacturing Polymer-Dispersed Liquid Crystal Film The PDLC film described in Section A can be manufactured by any appropriate manufacturing method. The method for manufacturing the PDLC film described in Section A includes, in this order, for example: (Step I) applying a coating liquid containing a polymer matrix-forming resin, a liquid crystal component, a dichroic dye, and a solvent to the surface of a release liner to form a coating layer; (Step II) drying the coating layer to form a primary PDLC layer on the release liner, the primary PDLC layer including a polymer matrix and droplets dispersed in the polymer matrix and containing the liquid crystal component and the dichroic dye; (Step III) stretching the primary PDLC layer to obtain a secondary PDLC layer; (Step IV) obtaining a laminate of the secondary PDLC layer and a first transparent conductive film; and (Step V) laminating a second transparent conductive film on the side of the secondary PDLC layer opposite to the side where the first transparent conductive film is disposed.

[0058] B-1. Step I In step I, a coating liquid containing a polymer matrix-forming resin, a liquid crystal component, a dichroic dye, and a solvent is applied to the surface of a release liner to form a coating layer.

[0059] The coating liquid is preferably an emulsion in which liquid crystal particles containing a liquid crystal component and a dichroic dye are dispersed in a solvent (hereinafter, this may be referred to as an "emulsion coating liquid"). In one embodiment, the coating liquid is an emulsion in which polymer matrix-forming resin particles and liquid crystal particles containing a liquid crystal component and a dichroic dye are dispersed in a solvent. The emulsion coating liquid may further contain any appropriate additive depending on the purpose.

[0060] The solvent is preferably water or a mixture of water and a water-miscible organic solvent. Examples of the water-miscible organic solvent include C1-3 alcohol, acetone, and DMSO. The polymer matrix-forming resin, liquid crystal component, dichroic dye, and additives, as well as their blending ratios, are as described in Section A.

[0061] The average particle size of the liquid crystal particles is, for example, 0.01 μm to 40 μm, preferably 0.05 μm to 30 μm, more preferably 0.1 μm to 15 μm, and even more preferably 0.15 μm to 10 μm. The average particle size of the liquid crystal particles can correspond to the average particle size of the liquid crystal droplets in the primary PDLC layer. If the average particle size of the liquid crystal particles is within this range, the average particle size of the liquid crystal droplets in the secondary PDLC layer can be set to a desired range. Note that the average particle size of the liquid crystal particles is a volume average particle size. The average particle size of the liquid crystal particles can be measured, for example, using a laser diffraction particle size distribution measurement device.

[0062] The particle size of the liquid crystal particles preferably has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the liquid crystal particles may be, for example, less than 0.4, preferably 0.35 or less, and more preferably 0.3 or less.

[0063] The average particle size of the resin particles for forming a polymer matrix is ​​preferably 10 nm to 500 nm, more preferably 30 nm to 300 nm, and even more preferably 50 nm to 200 nm. Two or more types of resin particles differing in type and / or average particle size may be used. The average particle size of the resin particles for forming a polymer matrix means the volume-average median size and can be measured using a dynamic light scattering particle size distribution analyzer.

[0064] The emulsion coating liquid can be prepared, for example, by mixing a resin emulsion containing polymer matrix-forming resin particles or a resin solution containing a polymer matrix-forming resin with a liquid crystal emulsion containing liquid crystal particles and optional additives (e.g., a dispersant, a leveling agent, a crosslinking agent). If necessary, a solvent may be added during mixing. Alternatively, the emulsion coating liquid can be prepared by adding the liquid crystal component, the dichroic dye, the polymer matrix-forming resin, and optional additives to a solvent and mechanically dispersing them.

[0065] The resin emulsion and liquid crystal emulsion can be prepared by, for example, a mechanical emulsification method, a microchannel method, a membrane emulsification method, or the like. Among these, it is preferable to prepare the liquid crystal emulsion by the membrane emulsification method. The membrane emulsification method can suitably produce an emulsion with a uniform particle size distribution. For details of the membrane emulsification method, reference can be made to the disclosures of JP-A-4-355719, JP-A-2015-40994, and the like (these are incorporated herein by reference).

[0066] The solid content of the emulsion coating liquid may be, for example, 20% to 60% by weight, and preferably 30% to 50% by weight.

[0067] The viscosity of the emulsion coating solution can be appropriately adjusted to ensure successful application to the release liner. The viscosity of the emulsion coating solution during application is preferably 20 mPa·s to 400 mPa·s, more preferably 30 mPa·s to 300 mPa·s, and even more preferably 40 mPa·s to 200 mPa·s. If the viscosity is less than 20 mPa·s, solvent convection becomes significant during solvent drying, potentially resulting in an unstable thickness of the primary PDLC layer (and consequently, the secondary PDLC layer). Furthermore, if the viscosity exceeds 400 mPa·s, the beading of the emulsion coating solution may become unstable. The viscosity of the emulsion coating solution can be measured, for example, using an Anton Paar MCR302 rheometer. The viscosity used here refers to the shear viscosity measured at 20°C and a shear rate of 1000 (1 / s).

[0068] The release liner may have a configuration in which a release agent layer is provided on at least one side of a film substrate. The release liner may be in the form of a sheet or a long strip. The release liner is preferably in the form of a long strip. In this specification, "long strip" means a long, slender shape in which the length is sufficiently long relative to the width, and includes, for example, a long, slender shape in which the length is 10 times or more, preferably 20 times or more, relative to the width. A long film can be wound into a roll.

[0069] The film substrate is not limited as long as it is applicable to the stretching treatment described later, and a resin film is preferably used. Examples of resins that form the resin film include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins. Among these, polyester resins such as PET are particularly preferred.

[0070] Examples of materials for forming the release layer include silicone-based release agents, fluorine-based release agents, long-chain alkyl-based release agents, fatty acid amide-based release agents, etc. The release agents can be used alone or in combination of two or more.

[0071] The thickness of the release liner is, for example, 10 μm to 200 μm, preferably 25 μm to 150 μm, and the thickness of the release agent layer is, for example, 0.001 μm to 10 μm, preferably 0.03 μm to 7 μm.

[0072] The emulsion coating liquid is typically applied to the release agent layer surface of the release liner. Any appropriate method can be used as the coating method. Examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (such as comma coating). Of these, roll coating is preferred. For example, the description of JP 2019-5698 A can be referenced for coating by roll coating using a slot die.

[0073] The thickness of the coating layer is preferably 3 μm to 200 μm, more preferably 5 μm to 150 μm, and even more preferably 10 μm to 100 μm.

[0074] B-2. Step II In step II, the coating layer is dried to form a primary PDLC layer on the release liner, the primary PDLC layer comprising a polymer matrix and droplets dispersed in the polymer matrix, the droplets containing a liquid crystal component and a dichroic dye. The solvent is removed from the coating layer by drying, leaving behind the polymer matrix-forming resin and liquid crystal particles containing the liquid crystal component and the dichroic dye. As a result, a primary PDLC layer having a structure in which liquid crystal droplets are dispersed in a polymer matrix is ​​formed.

[0075] The coating layer can be dried by any appropriate method. Specific examples of the drying method include natural drying, heat drying, hot air drying, etc. When the coating liquid contains a crosslinking agent, a crosslinked structure of the polymer matrix can be formed during drying.

[0076] The drying temperature is preferably 20° C. to 150° C., more preferably 25° C. to 80° C. The drying time is preferably 1 minute to 100 minutes, more preferably 2 minutes to 10 minutes.

[0077] The thickness of the primary PDLC layer is preferably 1 μm to 100 μm, more preferably 3 μm to 60 μm, and even more preferably 5 μm to 40 μm.

[0078] In this manner, a laminate having a [release liner / primary PDLC layer] configuration is obtained. If necessary, a separate release liner (second release liner) may be laminated on the primary PDLC layer side of the laminate. By laminating the second release liner, the primary PDLC layer can be suitably protected. Furthermore, the laminate can be stored in a roll. The second release liner can be the same as the release liner (first release liner) used in Step I.

[0079] B-3. ​​Step III In Step III, the primary PDLC layer is stretched to obtain a secondary PDLC layer. Stretching reduces the layer thickness and deforms the liquid crystal droplets, forming a secondary PDLC layer containing liquid crystal droplets that are flat in the thickness direction. Stretching also causes the liquid crystal component and dichroic dye in the liquid crystal droplets to be oriented in-plane, potentially improving the light absorption efficiency in the colored state. The secondary PDLC layer may correspond to the PDLC layer containing liquid crystal droplets that are flat in the thickness direction in the PDLC film described in Section A.

[0080] The primary PDLC layer may be stretched in a laminated state with a release liner, or may be stretched independently after being peeled off from the release liner. The laminate to be stretched may have a configuration of [first release liner / primary PDLC layer], [second release liner / primary PDLC layer], or [first release liner / primary PDLC layer / second release liner].

[0081] When a laminate of a primary PDLC layer and a release liner is stretched, the laminate may have a configuration in which the edge of the release liner protrudes outward beyond the edge of the primary PDLC layer. A laminate having such a configuration can be stretched by holding the edge of the release liner, thereby preventing damage to the appearance of the secondary PDLC layer after stretching. A laminate having such a configuration can be obtained, for example, by applying a coating liquid to the edge of the release liner as an uncoated area in step I, and then removing the edge of the primary PDLC layer formed on the release liner with adhesive tape in step II.

[0082] The stretching direction is not limited. The stretching may be, for example, longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and transverse biaxial stretching, or oblique stretching. Furthermore, it may be free-end stretching, fixed-end stretching, or a combination thereof. The longitudinal and transverse biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. Biaxial stretching can suitably obtain liquid crystal droplets that have a small ratio of the major axis to the minor axis in a planar view (major axis / minor axis) and are flat in the thickness direction, and can improve the uniformity of in-plane haze, total light transmittance, etc.

[0083] The stretching ratio can be appropriately set depending on the purpose. The stretching ratio is, for example, 1.05 times or more, preferably 1.1 to 10 times, and more preferably 1.2 to 5 times. In the case of longitudinal and transverse biaxial stretching, it is preferable that the longitudinal stretching ratio and the transverse stretching ratio are approximately the same. The ratio between the two (longitudinal stretching ratio / transverse stretching ratio) can be, for example, 0.9 to 1.1, and preferably 0.95 to 1.05.

[0084] The stretching temperature may be any temperature at which the primary PDLC layer or the laminate of the primary PDLC layer and the release liner can be stretched, and is, for example, the glass transition temperature (Tg) of the polymer matrix-forming resin −50° C. to Tg + 200° C., preferably Tg − 20° C. to Tg + 150° C.

[0085] B-4. Step IV In Step IV, a laminate of the secondary PDLC layer and a first transparent conductive film is obtained. When the laminate of the primary PDLC layer and release liner is stretched in Step III, the secondary PDLC layer is transferred from the release liner to the first transparent conductive film. This results in a laminate having a [first transparent conductive film / secondary PDLC layer] configuration. The first transparent conductive film is as described in Section A.

[0086] The lamination (transfer) of the secondary PDLC layer onto the first transparent conductive film may be performed via an adhesive layer or without an adhesive layer. The adhesive layer is typically an adhesive layer or a pressure-sensitive adhesive layer. When an adhesive layer is not used, the lamination of the first transparent conductive film is preferably performed using a laminator while applying a lamination pressure of 0.006 MPa / m to 7 MPa / m, more preferably 0.06 MPa / m to 0.7 MPa / m, from the viewpoint of obtaining sufficient adhesion.

[0087] B-5. Step V In step V, a second transparent conductive film is laminated on the side of the secondary PDLC layer opposite to the side on which the first transparent conductive film is disposed in the laminate. The second transparent conductive film is as described in section A. The PDLC film thus obtained, having a structure of [first transparent conductive film / secondary PDLC layer / second transparent conductive film], can correspond to the PDLC film described in section A.

[0088] The second transparent conductive film may be laminated onto the secondary PDLC layer via an adhesive layer or without an adhesive layer. The adhesive layer is typically an adhesive layer or a pressure-sensitive adhesive layer. When an adhesive layer is not used, the second transparent conductive film is preferably laminated using a laminator while applying a lamination pressure of 0.006 MPa / m to 7 MPa / m, more preferably 0.06 MPa / m to 0.7 MPa / m, from the viewpoint of obtaining sufficient adhesion.

[0089] The PDLC film of the present invention is suitably used in various applications such as displays such as advertisements and guide boards, and smart windows.

[0090] 100 PDLC film 10 First transparent conductive film 20 PDLC layer 22 Polymer matrix 23 Liquid crystal component 24 Dichroic dye 25 Liquid crystal droplets 30 Second transparent conductive film

Claims

1. A polymer dispersed liquid crystal film comprising, in this order, a first transparent conductive film, a polymer dispersed liquid crystal layer, and a second transparent conductive film, wherein the polymer dispersed liquid crystal layer comprises a polymer matrix and droplets dispersed in the polymer matrix, the droplets containing a liquid crystal component and a dichroic dye, and the average flatness of the droplets is 0.3 or more.

2. The polymer dispersed liquid crystal film according to claim 1, wherein the average particle diameter of the droplets in a cross section perpendicular to the main surface is 0.1 μm or more and 10 μm or less.

3. The polymer dispersed liquid crystal film according to claim 1, wherein the content of said dichroic dye in said polymer dispersed liquid crystal layer is 0.5% by weight or more.

4. The polymer dispersed liquid crystal film according to claim 1, wherein the thickness of the polymer dispersed liquid crystal layer is 30 μm or less.

5. The polymer dispersed liquid crystal film according to claim 1, which has a total light transmittance of 20% or less when no voltage is applied.

6. The polymer dispersed liquid crystal film according to claim 1, which has a total light transmittance of 20% or more when a voltage is applied.

7. The polymer dispersed liquid crystal film according to claim 1, which has a haze of 20% or less when a voltage is applied.

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