Polymer dispersed liquid crystal film

Abstract

To provide a PDLC film capable of switching between a colored state and a transparent state, with improved transparency at the colored state.SOLUTION: A polymer dispersion type liquid crystal film includes a first transparent conductive film, a polymer dispersion type liquid crystal layer and a second transparent conductive film in this order. The polymer dispersion type liquid crystal layer includes a polymer matrix and droplets dispersed in the polymer matrix each including a liquid crystal component and a dichroic dye. An average particle diameter of the droplets is 1 μm or less, and clarity in the colored state is 90 or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A PDLC film, which has a polymer-dispersed liquid crystal (PDLC) layer containing a polymer matrix and liquid crystal droplets between a pair of transparent electrode layers, can change the degree of scattering of light transmitted through the PDLC layer depending on the amount of applied voltage. For example, a PDLC film can switch between a light-scattering state (scattering state) and a light-transmitting state (transparent state) by switching between an applied voltage state and an unapplied voltage state (Patent Document 1). Taking advantage of this function, PDLC films are increasingly being applied as light-control films that can improve privacy or security to windows, walls, partitions, and other surfaces in vehicles such as cars and trains, offices, commercial facilities, and homes.

[0003] In the above-mentioned PDLC film, if a dichroic dye is contained in the liquid crystal component droplets, it is possible to switch between a colored state that absorbs light of at least some wavelengths and a transparent state that transmits light by switching between a voltage-applied state and a voltage-unapplied state (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-189123 [Patent Document 2] International Publication No. 2022 / 186062 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional PDLC films using dichroic dyes tend to have low transparency in the colored state. Therefore, for applications requiring transparency and clear visibility, there is a demand for PDLC films with improved transparency in the colored state.

[0006] The present invention has been made to solve the above-mentioned problems, and its main object is to provide a PDLC film that can be switched between a colored state and a transparent state and has improved transparency in the colored state. [Means for solving the problem]

[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 particle size of 1 μm or less and a clarity in a colored state of 90 or more. [2] In the polymer dispersed liquid crystal film according to the above [1], the droplets may have an average particle size of 0.01 μm or more and less than 0.38 μm. [3] In the polymer dispersed liquid crystal film according to the above [1] or [2], the birefringence of the liquid crystal component may be 0.25 or less. [4] In the polymer dispersed liquid crystal film according to any one of [1] to [3] above, the weight ratio (former:latter) of the content of the polymer matrix in the polymer dispersed liquid crystal layer to the total content of the liquid crystal component and the dichroic dye may be 10:90 to 70:30. [5] In the polymer dispersed liquid crystal film according to any one of the above [1] to [4], the thickness of the polymer dispersed liquid crystal layer may be 30 μm or less. [6] In the polymer dispersed liquid crystal film according to any one of [1] to [5] above, the total light transmittance in the colored state may be 50% or less. [7] In the polymer dispersed liquid crystal film according to any one of [1] to [6] above, the haze in the colored state may be 80% or less. [Effects of the Invention]

[0008] SUMMARY OF THE INVENTION According to an embodiment of the present invention, a PDLC film is provided that is switchable between a colored state and a transparent state and has improved transparency in the colored state. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of a PDLC film in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In this specification, the term "to" indicating a range of values ​​includes the upper and lower limits.

[0011] A. Polymer dispersed liquid crystal film A polymer dispersed liquid crystal film according to an embodiment of the present invention comprises, 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 (hereinafter sometimes referred to as "liquid crystal droplets") dispersed in the polymer matrix and containing a liquid crystal component and a dichroic dye, wherein the droplets have an average particle size of 1 μm or less and a clarity of 90 or more in a colored state.

[0012] As described above, the appearance of the PDLC film changes depending on the applied voltage. In one embodiment, the PDLC film is transparent when a voltage is applied and colored when no voltage is applied (normal mode). In another embodiment, the PDLC film is colored when a voltage is applied and transparent when no voltage is applied (reverse mode).

[0013] FIG. 1 is a schematic cross-sectional view illustrating the configuration of an example of a normal-mode PDLC film according to an embodiment of the present invention. FIG. 1(a) shows the PDLC layer in a state where no voltage is applied (colored state), and FIG. 1(b) shows the PDLC layer in a state where a voltage is applied (transparent state). The PDLC film 100 includes, in 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 crystals containing a liquid crystal component 23 and a dichroic dye 24. As shown in FIG. 1(a), when no voltage is applied, the liquid crystal component 23 and the dichroic dye 24 in the liquid crystal droplets 25 are misaligned. Light is absorbed by the dichroic dye 24, resulting in the PDLC film 100 being in a colored state. 1(b), when a voltage is applied, the liquid crystal component 23 is oriented along the electric field direction, and the dichroic dye 24 is also oriented following the liquid crystal component 23. As a result, the refractive index of the liquid crystal droplets 25 and the refractive index of the polymer matrix 22 become the same, and the PDLC film 100 becomes transparent.

[0014] Although not shown, in a reverse mode PDLC film, an alignment film is provided on the 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 to form a transparent state, and when a voltage is applied, the alignment state of the liquid crystal component 23 and dichroic dye 24 changes, resulting in a colored state.

[0015] The clarity of the PDLC film in the colored state is, for example, 90 or more, preferably 92 or more, more preferably 95 or more, and even more preferably 97 or more. The upper limit of clarity is 100. Clarity corresponds to the narrow-angle scattering degree, and is the transmittance in an angular range of ±2.5° relative to the direction of travel of parallel light incident on the PDLC film. High clarity means that the boundaries of an image viewed through the PDLC film are clear. Clarity is expressed as the amount of light L that, among the light transmitted through the PDLC film, travels straight along the optical axis of the parallel light incident on the PDLC film. CThe amount of narrow-angle scattered light whose angle with respect to the optical axis of the parallel light is within ±2.5° is defined as the light amount L R When this is the case, it is calculated using the following formula (1). 100×(L C -L R ) / (L C +L R ) … Formula (1)

[0016] The total light transmittance of the PDLC film in the colored state is, for example, 50% or less, and may be 40% or less, 30% or less, 20% or less, or 10% or less, and may be, for example, 0.5% or more, or 1% or more. The total light transmittance of the PDLC film in the transparent state is, for example, 15% or more, 20% or more, 30% or more, or 50% or more, and may be, for example, 99% or less. The difference in total light transmittance between the transparent and colored states of the PDLC film is, for example, 10% or more, 20% or more, or 30% or more. The total light transmittance can be measured according to JIS K 7361.

[0017] The haze of the PDLC film in the colored state is, for example, 80% or less, and may be 60% or less, 50% or less, or 45% or less, and may be, for example, 5% or more. The haze of the PDLC film in the transparent state is, for example, 30% or less, and may be 20% or less, 10% or less, or 5% or less, and may be, for example, 0.1% or more. The difference in haze between the transparent and colored states of the PDLC film is, for example, 10% or more, and may be 20% or more, 30% or more, or 40% or more. Haze can be measured according to JIS K 7136.

[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 300 V, and preferably 10 V to 200 V. In this specification, "when a voltage is applied" 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 150 V is applied.

[0019] The total thickness of the PDLC film is, for example, 30 μm to 250 μm, and 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 primarily 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. Among these, polyester-based resins, cycloolefin-based resins, and acrylic resins are preferred. These resins are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and the like. The above-mentioned thermoplastic resins may be used alone or in combination of two or more. Optical films used in polarizing plates, such as low-retardation substrates, high-retardation substrates, retardation plates, absorptive polarizing films, and polarized selective reflection films, can also be used as the first transparent substrate.

[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 can be formed using a metal oxide such as indium tin oxide (ITO), zinc oxide (ZnO), or tin oxide (SnO2). In this case, the metal oxide may be an amorphous metal oxide or a crystallized metal oxide. The first transparent electrode layer can also be formed from metal nanowires such as silver nanowires (AgNWs), carbon nanotubes (CNTs), 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 can 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 the transparent 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 provided 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 heat treatment at, for example, 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 average particle size of the liquid crystal droplets is typically 1 μm or less, e.g., 0.5 μm or less. A PDLC layer containing small-sized liquid crystal droplets exhibits low scattering, and therefore, a PDLC film with high clarity can be obtained by setting the average particle size of the liquid crystal droplets to 1 μm or less. To further reduce scattering, the average particle size of the liquid crystal droplets is preferably equal to or less than the wavelength of visible light. Specifically, the average particle size of the liquid crystal droplets is preferably less than 0.38 μm, more preferably less than 0.3 μm, even more preferably less than 0.2 μm, even more preferably 0.18 μm or less, even more preferably 0.15 μm or less, and even more preferably 0.12 μm or less. The lower limit of the average particle size of the liquid crystal droplets is not limited as long as the effects of the present invention are obtained, and may be, for example, 0.01 μm or more or 0.05 μm or more. The average particle size of the liquid crystal droplets is a volume average particle size, and can be determined, for example, by the method described in the Examples.

[0033] The particle size of the liquid crystal droplets preferably has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the particle size of the liquid crystal droplets may be, for example, less than 0.4, preferably 0.35 or less, and more preferably 0.3 or less. The coefficient of variation can be calculated using the following formula: CV value = standard deviation of particle size distribution of liquid crystal droplets / average particle size

[0034] 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, etc. The resin for forming the polymer matrix preferably has a refractive index similar to that of the liquid crystal component.

[0035] Specific examples of the polymer matrix-forming resin include 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.

[0036] As the liquid crystal component, any appropriate liquid crystal compound can be used alone or in combination of two or more. The birefringence (Δn=ne-no; ne is the extraordinary refractive index, no is the ordinary refractive index) of the liquid crystal component at a wavelength of 589 nm is, for example, 0.25 or less. From the viewpoint of obtaining a PDLC film with high clarity, the birefringence is preferably 0.2 or less, more preferably 0.15 or less, for example, 0.12 or less, or may be, for example, 0.1 or less. The birefringence is, for example, 0.01 or more, 0.05 or more, or 0.08 or more. By using a liquid crystal component having the above birefringence, the scattering property of the PDLC layer when no voltage is applied can be reduced, resulting in a PDLC film with high clarity.

[0037] The dielectric anisotropy of the liquid crystal component may be positive or negative. 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 can achieve excellent transparency in the transparent state.

[0038] 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.

[0039] 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 or negative Δε. The dichroic dye itself may exhibit liquid crystallinity. The dichroic dye may be used alone or in combination of two or more.

[0040] 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, lightfastness, and the like, it is preferable that the dichroic dye contains anthraquinone dyes or azo dyes. For example, the azo dyes, anthraquinone dyes, or mixtures thereof described in "Liquid Crystal Device Handbook," edited by the 142nd Committee of the Japan Society for the Promotion of Science, Japan Industrial Newspaper Co., Ltd. (1989), pages 192-196 and 724-730, can be used. Various dichroic dyes are commercially available, and these can be used as appropriate.

[0041] The PDLC layer may further contain any appropriate component, if necessary, such as a surfactant, a leveling agent, a crosslinking agent, a dispersion stabilizer, etc.

[0042] 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.

[0043] 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, relative to 100 parts by weight of the liquid crystal component.

[0044] 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.

[0045] 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.

[0046] The thickness of the PDLC layer is preferably 40 μm or less, more preferably 30 μm or less, for example, 25 μm or less, or for example, 20 μm or less, and is preferably 2 μm or more, more preferably 3 μm or more, for example, 5 μm or more, or for example, 10 μm or more. When the thickness of the PDLC layer is within the above range, a PDLC film with high clarity and high colorability can be suitably obtained.

[0047] 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.

[0048] 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 / □.

[0049] 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%.

[0050] 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.

[0051] 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 structure as the first transparent conductive film, or may have a different structure.

[0052] B. Manufacturing method of polymer dispersed liquid crystal film The PDLC film described in Section A can be produced by any suitable production method. The PDLC film described in Section A can be produced by, for example, mixing a liquid crystal component, a dichroic dye, and a dispersion medium to prepare a liquid crystal emulsion containing particles containing the liquid crystal component and the dichroic dye (Step A); mixing the liquid crystal emulsion with a polymer matrix-forming resin to prepare a coating liquid containing the particles (step B); applying the coating liquid to a first transparent conductive film to obtain a coating layer (step C); drying the coated layer to obtain a PDLC layer containing a polymer matrix and droplets containing the liquid crystal component and the dichroic dye dispersed in the polymer matrix (step D); and laminating a second transparent conductive film on the PDLC layer (Step E); Includes.

[0053] B-1. Process A In step A, a liquid crystal component, a dichroic dye, and a dispersion medium are mixed to prepare a liquid crystal emulsion containing particles containing the liquid crystal component and the dichroic dye (hereinafter, sometimes referred to as "liquid crystal particles").

[0054] The dispersion medium 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 liquid crystal component and dichroic dye are as described in Section A.

[0055] The content of the liquid crystal component in the liquid crystal emulsion is, for example, 30% to 70% by weight, and preferably 40% to 60% by weight.

[0056] The content of the dichroic dye in the liquid crystal emulsion 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, relative to 100 parts by weight of the liquid crystal component.

[0057] The average particle size of the liquid crystal particles is typically 1 μm or less, e.g., 0.5 μm or less, preferably less than 0.38 μm, more preferably less than 0.3 μm, even more preferably less than 0.2 μm, even more preferably 0.18 μm or less, even more preferably 0.15 μm or less, even more preferably 0.12 μm or less, and may be, for example, 0.01 μm or more or 0.05 μm or more. The particle size of the liquid crystal droplets in the PDLC layer may depend on the particle size of the liquid crystal particles in the liquid crystal emulsion. Therefore, if the average particle size of the liquid crystal particles in the liquid crystal emulsion is within the above range, the average particle size of the liquid crystal droplets in the PDLC layer can be adjusted to the desired range. The average particle size of the liquid crystal particles refers to the volume-average median diameter and can be measured using a dynamic light scattering particle size distribution analyzer.

[0058] 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.

[0059] Liquid crystal emulsions can be prepared by, for example, mechanical emulsification, microchannel emulsification, membrane emulsification, etc. Preferably, liquid crystal emulsions are prepared by mechanical emulsification or membrane emulsification. Mechanical emulsification can efficiently produce liquid crystal emulsions with small particle sizes. Mechanical emulsification can be performed using known dispersion / mixing devices such as homomixers and homogenizers, and preferably using homogenizers such as high-pressure homogenizers and ultrasonic homogenizers. Furthermore, membrane emulsification can suitably produce emulsions with a uniform particle size distribution. For details of membrane emulsification, see the disclosures of JP-A-4-355719 and JP-A-2015-40994 (which are incorporated herein by reference).

[0060] The order in which the liquid crystal component, dichroic dye, and dispersion medium are mixed is not particularly limited. For example, the liquid crystal component and the dichroic dye may be mixed together, and the resulting mixture may then be mixed with the dispersion medium. Alternatively, the three may be added and mixed simultaneously.

[0061] B-2.Process B In step B, the liquid crystal emulsion obtained in step A is mixed with a polymer matrix-forming resin to prepare a coating liquid containing the liquid crystal particles. The coating liquid may contain any other components as needed. Examples of the optional components include surfactants, leveling agents, crosslinking agents, and dispersion stabilizers. These optional components may be added to the liquid crystal emulsion in step A depending on the purpose.

[0062] The polymer matrix resin is as described in Section A. The polymer matrix resin is mixed with the liquid crystal emulsion, for example, as a resin dispersion in which polymer matrix resin particles are dispersed in a dispersion medium, or as a resin solution in which the polymer matrix resin is dissolved in a solvent. In this case, the dispersion medium for the resin dispersion or the solvent for the resin solution may be the same as the dispersion medium used in preparing the liquid crystal emulsion.

[0063] The average particle diameter 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 diameter may be used. The average particle diameter of the resin particles for forming a polymer matrix means the volume-average median diameter and can be measured using a dynamic light scattering particle size distribution analyzer.

[0064] The particle size of the liquid crystal particles in the coating solution is substantially the same as that in the liquid crystal emulsion. Therefore, the average particle size (volume average particle size) of the liquid crystal particles in the coating solution is typically 1 μm or less, for example, 0.5 μm or less, preferably less than 0.38 μm, more preferably less than 0.3 μm, even more preferably less than 0.2 μm, even more preferably 0.18 μm or less, even more preferably 0.15 μm or less, even more preferably 0.12 μm or less, and may be, for example, 0.01 μm or more or 0.05 μm or more.

[0065] The content of the liquid crystal component in the solid content of the coating liquid is, for example, 30% to 90% by weight, preferably 35% to 85% by weight, and more preferably 40% to 80% by weight.

[0066] 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 coating liquid is, for example, 10:90 to 70:30, preferably 15:85 to 65:35, and more preferably 20:80 to 60:40.

[0067] The total content of the polymer matrix, liquid crystal component, and dichroic dye in the solid content of the coating liquid 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.

[0068] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. The content of the surfactant is preferably 1 to 15 parts by weight, more preferably 2 to 10 parts by weight, per 100 parts by weight of the solid content of the coating liquid.

[0069] Examples of the leveling agent include acrylic leveling agents, fluorine-based leveling agents, silicone-based leveling agents, etc. The content of the leveling agent is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the solid content of the coating liquid.

[0070] Examples of the crosslinking agent include an aziridine-based crosslinking agent, an isocyanate-based crosslinking agent, etc. The content of the crosslinking agent is preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight, relative to 100 parts by weight of the solid content of the coating liquid.

[0071] The solid content concentration of the coating liquid can be, for example, 20% by weight to 60% by weight, and preferably 30% by weight to 50% by weight.

[0072] B-3.Process C In step C, the coating liquid prepared in step B is applied to the first transparent conductive film to obtain a coating layer.

[0073] The coating liquid is typically applied to the surface of the first transparent conductive film on the transparent electrode layer side. The first transparent conductive film is as described in Section A.

[0074] The viscosity of the coating liquid during application is preferably 20 mPas to 400 mPas, more preferably 30 mPas to 300 mPas, and even more preferably 40 mPas to 200 mPas. If the viscosity is less than 20 mPas, convection of the dispersion medium becomes significant when the dispersion medium is dried, which may result in an unstable thickness of the PDLC layer. If the viscosity exceeds 400 mPas, the coating liquid bead may become unstable. The viscosity of the coating liquid can be measured, for example, using an Anton Paar MCR302 rheometer. The viscosity used here is the shear viscosity value at 20°C and a shear rate of 1000 (1 / s).

[0075] Any appropriate method can be used as the coating method. For example, roll coating, spin coating, bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), etc. can be mentioned. Among them, roll coating is preferred. For example, the description of JP-A-2019-5698 can be referred to for coating by roll coating using a slot die.

[0076] The thickness of the coating layer is preferably 1 μm to 100 μm, more preferably 2 μm to 90 μm, and even more preferably 5 μm to 75 μm.

[0077] B-4.Process D In step D, the coating layer is dried to obtain a PDLC layer containing a polymer matrix and droplets of liquid crystal components dispersed in the polymer matrix. The dispersion medium is removed from the coating layer by drying, leaving behind the polymer matrix-forming resin and particles containing the liquid crystal components, resulting in the formation of a PDLC layer having a structure in which liquid crystal droplets are dispersed in a polymer matrix.

[0078] 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.

[0079] 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.

[0080] B-5.Process E In step E, a second transparent conductive film is laminated on the PDLC layer, thereby obtaining a PDLC film having the first transparent conductive film, the PDLC layer, and the second transparent conductive film in this order.

[0081] The second transparent conductive film is as described in Section A. The second transparent conductive film is typically laminated onto the PDLC layer so that the second transparent electrode layer faces the PDLC layer. To ensure sufficient adhesion, the lamination 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. [Example]

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

[0083] (1) Thickness Measurement was carried out using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). (2) Volume average particle size of liquid crystal particles in liquid crystal emulsion A measurement sample was prepared by adding a few drops of liquid crystal emulsion to 100 mL of water. Using a dynamic light scattering particle size distribution analyzer (Microtrac, device name "Nanotrac150"), the measurement sample was placed in the measurement holder of the device, and measurements were performed after checking on the device monitor that the concentration was measurable. (3) Average particle size of resin particles A measurement sample was prepared by adding a few drops of the resin dispersion to 100 mL of water. Using a dynamic light scattering particle size distribution analyzer (Microtrac, device name "Nanotrac150"), the measurement sample was placed in the measurement holder of the device, and measurements were performed after checking on the device monitor that the concentration was measurable. (4) Hayes Measurement was carried out in accordance with JIS K 7136 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH4000"). (5) Total light transmittance Measurement was carried out in accordance with JIS K 7361 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH4000"). (6) Clarity The haze was measured using a haze meter (manufactured by BYK-GARDNER, product name "haze-gard i") according to the method specified by the manufacturer. (7) Average particle size of liquid crystal droplets in the PDLC layer The PDLC film was sliced ​​horizontally under a cooled environment, and the exposed horizontal cross-section of the PDLC layer was smoothed using a microtome. The horizontal cross-section of the PDLC layer was then observed using a scanning electron microscope (SEM) to obtain cross-sectional SEM images. The Heywood diameters of all liquid crystal droplets in a 30 μm × 20 μm area were calculated from the cross-sectional areas. The volume-average particle diameter (median diameter) was calculated by taking statistics weighted by the estimated volume for each equivalent diameter. (8) Birefringence of liquid crystal components Values ​​disclosed by the manufacturers of the liquid crystal components were used.

[0084] [Example 1] (First and second transparent conductive films) An ITO layer was formed by sputtering on one surface of a PET substrate (thickness: 50 μm) to obtain a transparent conductive film having a structure of [transparent substrate / transparent electrode layer].

[0085] (Preparation of Liquid Crystal Emulsion) A liquid crystal emulsion was prepared by mixing 27.9 parts of a liquid crystal component containing two or more liquid crystal compounds (JNC Corporation, product name "JC-5175XX"; birefringence Δn = 0.09 (ne = 1.569, no = 1.479), dielectric anisotropy Δε = 7.9, viscosity = 32.2 mPa s), 0.26 parts of a dichroic dye (Hayashibara Co., Ltd., product name "G-470"), 0.53 parts of a dichroic dye (Hayashibara Co., Ltd., product name "NKX-3739"), 1.31 parts of a dichroic dye (Hayashibara Co., Ltd., product name "NKX-3708"), 67 parts of purified water, and 3 parts of a surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") in a high-pressure homogenizer. The average particle size of the liquid crystal particles in the resulting liquid crystal emulsion was 170 nm.

[0086] (Preparation of coating liquid) An emulsion coating liquid (solid concentration: 30 wt%) was obtained by mixing 47.6 parts of the above liquid crystal emulsion, 32 parts of an aqueous dispersion of polyether-based polyurethane resin (manufactured by DSM, product name "NeoRezR967", average polymer particle size: 80 nm, CV value = 0.27, solid content: 40 wt%), 0.1 parts of a leveling agent (manufactured by DIC, product name "F-444"), 1 part of a crosslinking agent (tris[3-(2-methylaziridin-1-yl)propionic acid] = propylidinetrimethyl), and 19.3 parts of pure water.

[0087] (Production of PDLC film) The emulsion coating liquid was applied to the ITO layer surface of the first transparent conductive film and dried at 40°C to form a 16µm thick PDLC layer. A laminating pressure of 0.4MPa / m was then applied using a laminator to laminate the second transparent conductive film on top of the PDLC layer, with the ITO layer facing the PDLC layer. This resulted in a PDLC film.

[0088] [Examples 2 to 8] PDLC films were obtained in the same manner as in Example 1, except that different types of liquid crystal components were used, liquid crystal emulsions with different average particle sizes of liquid crystal particles were prepared, and / or the thickness of the PDLC layer was changed, as shown in Table 1. The properties of the liquid crystal components used are as follows: ·Liquid crystal component (manufactured by JNC, product name "JC-5174XX", birefringence Δn=0.098 (ne=1.577, no=1.479), dielectric constant anisotropy Δε=11.8, viscosity=46.8mPa·s) ·Liquid crystal component (manufactured by JNC, product name "JC-5173XX", birefringence Δn=0.149 (ne=1.651, no=1.502), dielectric anisotropy Δε=10.0, viscosity=48.5mPa·s)

[0089] [Comparative Example 1] (First and second transparent conductive films) An ITO layer was formed by sputtering on one surface of a PET substrate (thickness: 50 μm) to obtain a transparent conductive film having a structure of [transparent substrate / transparent electrode layer].

[0090] (Preparation of liquid crystal emulsion) 27.9 parts of liquid crystal component (JNC Corporation, product name "JC-5174XX"), 0.26 parts of dichroic dye (Hayashibara Co., Ltd., product name "G-470"), 0.53 parts of dichroic dye (Hayashibara Co., Ltd., product name "NKX-3739"), 1.31 parts of dichroic dye (Hayashibara Co., Ltd., product name "NKX-3708"), 67 parts of purified water, and 3 parts of surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") were mixed and coarsely dispersed by stirring at 100 rpm for 10 minutes in a homogenizer. The coarse dispersion was passed through a separation membrane with a uniform particle size distribution (SPG Techno Corporation, "SPG Pumping Connector", pore size 5 μm) at room temperature from the outside to the inside of the membrane at a flow rate of 80 mL / min / cm. 2 This procedure was repeated 10 times. The volume average particle size of the liquid crystal particles in the resulting liquid crystal emulsion was 2.1 μm.

[0091] (Preparation of coating liquid) An emulsion coating liquid (solid concentration: 30 wt%) was obtained by mixing 47.6 parts of the above liquid crystal emulsion, 32 parts of an aqueous dispersion of polyether-based polyurethane resin (manufactured by DSM, product name "NeoRezR967", average polymer particle size: 80 nm, CV value = 0.27, solid content: 40 wt%), 0.1 parts of a leveling agent (manufactured by DIC, product name "F-444"), 1 part of a crosslinking agent (tris[3-(2-methylaziridin-1-yl)propionic acid] = propylidinetrimethyl), and 19.3 parts of pure water.

[0092] (Production of PDLC film) The emulsion coating liquid was applied to the ITO layer surface of the first transparent conductive film and dried at 40°C to form a 16µm thick PDLC layer. A laminating pressure of 0.4MPa / m was then applied using a laminator to laminate the second transparent conductive film on top of the PDLC layer, with the ITO layer facing the PDLC layer. This resulted in a PDLC film.

[0093] Comparative Example 2 As shown in Table 1, a PDLC film was obtained in the same manner as in Comparative Example 1, except that a different type of liquid crystal component was used.

[0094] <Visual transparency evaluation> The visual transparency was evaluated based on the visibility of the characters printed on plain paper in black ink when viewed visually through the PDLC film (colored state with no voltage applied) obtained in the Examples and Comparative Examples. The distance between the plain paper and the PDLC film was approximately 200 mm, and the distance from the observer's eye to the plain paper was 200 mm. The evaluation results, along with the clarity, total light transmittance, and haze of each PDLC film, are shown in Table 1. <Evaluation Criteria> Excellent: Very high transparency, allowing the text to be clearly read. Good: Transparency is moderately high and the text is visible. Poor: The transparency is low and the letters cannot be seen.

[0095] [Table 1]

[0096] As shown in Table 1, the PDLC films of the examples exhibited low scattering in the colored state and high clarity. [Industrial Applicability]

[0097] The PDLC film of the present invention is suitable for use in various applications such as displays such as advertisements and guide boards, and smart windows. [Explanation of symbols]

[0098] 100 PDLC film 10 First transparent conductive film 20 PDLC layers 22 Polymer matrix 23 Liquid crystal components 24 Dichroic dyes 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, the polymer dispersed liquid crystal layer includes a polymer matrix and droplets dispersed in the polymer matrix, the droplets including a liquid crystal component and a dichroic dye; The droplets have an average particle size of 1 μm or less, The haze in the colored state is 15.2% or more, The clarity in the colored state is 90 or more, The clarity is calculated by the following formula (1), where, among the light transmitted through the polymer dispersed liquid crystal film, the amount of light L C is the amount of straight light that travels straight with respect to the optical axis of the parallel light of the light incident on the polymer dispersed liquid crystal film, and the amount of light L R is the amount of narrow-angle scattered light whose angle with respect to the optical axis of the parallel light is within ±2.5°: 100×(L C −L R ) / (L C +L R ) Formula (1) Polymer dispersed liquid crystal film.

2. 2. The polymer dispersed liquid crystal film according to claim 1, wherein the droplets have an average particle size of 0.01 μm or more and less than 0.38 μm.

3. 2. The polymer dispersed liquid crystal film according to claim 1, wherein the birefringence of the liquid crystal component is 0.25 or less.

4. 2. The polymer dispersed liquid crystal film according to claim 1, wherein 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 polymer dispersed liquid crystal layer is 10:90 to 70:

30.

5. 2. The polymer dispersed liquid crystal film according to claim 1, wherein the thickness of the polymer dispersed liquid crystal layer is 30 [mu]m or less.

6. 2. The polymer dispersed liquid crystal film according to claim 1, wherein the total light transmittance in the colored state is 50% or less.

7. 2. The polymer dispersed liquid crystal film according to claim 1, wherein the haze in the colored state is 80% or less.

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