Polymer dispersion type 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 having a polymer dispersed liquid crystal (hereinafter sometimes referred to as "PDLC") layer containing a polymer matrix and droplets of liquid crystal components 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, the PDLC film can switch between a light scattering state (scattering state) and a light transmitting state (transparent state) by switching between a voltage applied state and a voltage non-applied state (Patent Document 1). By utilizing such a function, the PDLC film is being applied to windows, walls, partitions, etc. in vehicles such as cars and trains, offices, commercial facilities, residences, etc. as a light control film that can improve privacy or security.

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

[0004] [Patent Document 1] JP 2002-189123 A [Patent Document 2] International Publication 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, and therefore there is a demand for PDLC films with improved transparency in the colored state for applications requiring transparency and clear visibility.

[0006] The present invention has been made to solve the above-mentioned problems, and its main object is to provide a PDLC film that is switchable 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 average particle size of the droplets being 1 μm or less, and the clarity in a colored state being 90 or greater. [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 polymer dispersed liquid crystal layer may have a thickness of 30 μm or less. [6] In the polymer dispersed liquid crystal film according to any one of the above [1] to [5], the total light transmittance in a colored state may be 50% or less. [7] In the polymer dispersed liquid crystal film according to any one of [1] to [6] above, a haze in a colored state may be 80% or less. Effect of the Invention

[0008] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS OF THE PRESENT EMBODIMENTS 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 description of the drawings]

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

[0010] Hereinafter, preferred embodiments of the present invention will be described, 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, the polymer dispersed liquid crystal layer comprising 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 droplets having 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 for explaining the configuration of an example of a normal mode PDLC film according to an embodiment of the present invention, in which FIG. 1(a) shows a state in which no voltage is applied to the PDLC layer (colored state), and FIG. 1(b) shows a state in which a voltage is applied to the PDLC layer (transparent state). The PDLC film 100 includes 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, in this order. The liquid crystal droplets 25 are so-called guest-host liquid crystals that contain 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 not oriented, and 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 components 23 are oriented along the electric field direction, and the dichroic dye 24 is also oriented following the liquid crystal components 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 a 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 produce a transparent state, and when a voltage is applied, the alignment state of the liquid crystal component 23 and the 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° with respect to the traveling direction of the parallel light of the light incident on the PDLC film. High clarity means that the boundary of the image seen through the PDLC film is clear. Clarity is expressed as the amount of light L of the light that travels straight along the optical axis of the parallel light of the light that has passed through the PDLC film. CThe amount of narrow-angle scattered light with an angle of ±2.5° or less with respect to the optical axis of the parallel light is defined as the amount of light 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, and may be 1% or more. The total light transmittance of the PDLC film in the transparent state is, for example, 15% or more, and may be 20% or more, 30% or more, or 50% or more, and may be, for example, 99% or less. The difference in the total light transmittance between the transparent state and the colored state of the PDLC film is, for example, 10% or more, and may be 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, 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, for example, 0.1% or more. The difference in haze between the transparent state and the colored state of the PDLC film is, for example, 10% or more, and may be 20% or more, 30% or more, or 40% or more. The 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 has a first transparent substrate 12 and a first transparent electrode layer 14 provided on one side (the PDLC layer 20 side) of the first transparent substrate 12. The first transparent conductive film 10 may have a hard coat layer on one or both sides of the first transparent substrate 12, and may also have a refractive index adjusting layer between the first transparent substrate 12 and the first transparent electrode layer 14, as necessary.

[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 further 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 further 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 further preferably 80% or more.

[0024] The first transparent substrate may be formed using any suitable material. Typically, the first transparent substrate is a polymer film mainly composed of a thermoplastic resin. Examples of the thermoplastic resin include polyester resins; cycloolefin resins such as polynorbornene; acrylic resins; polycarbonate resins; and cellulose resins. Among them, polyester resins, cycloolefin resins, and acrylic resins are preferred. These resins are excellent in transparency, mechanical strength, thermal stability, and moisture shielding properties. The above thermoplastic resins may be used alone or in combination of two or more kinds. In addition, optical films such as those 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 further 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 further preferably 80% or more.

[0027] The first transparent electrode layer is made of, for example, indium tin oxide (ITO), zinc oxide (ZnO), 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 of a metal nanowire such as a silver nanowire (AgNW), a carbon nanotube (CNT), an organic conductive film, a metal layer, or a laminate thereof. Preferably, a transparent electrode layer containing ITO is formed. The 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 such a range, a PDLC film having a high total light transmittance in a 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, and preferably 15 nm or more.The thickness of the first transparent electrode layer is, for example, 50 nm or less, preferably 35 nm or less, and 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. The annealing is performed by, for example, heat treatment at 120°C to 300°C for 10 minutes 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 the structure 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, for example, 0.5 μm or less. Since a PDLC layer including liquid crystal droplets with a small particle size has low scattering properties, 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. From the viewpoint of further reducing scattering properties, it is preferable that the average particle size of the liquid crystal droplets is 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 from 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. It is preferable that the resin for forming the polymer matrix has a refractive index close to that of the liquid crystal component.

[0035] Specific examples of the polymer matrix forming resin include urethane resin, polyvinyl alcohol resin, polyethylene resin, polypropylene resin, acrylic resin, etc. These are preferably water-soluble resin or water-dispersible resin. 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 suitable liquid crystal compound can be used alone or in combination of two or more kinds. 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 birefringence, the scattering property of the PDLC layer when no voltage is applied can be reduced, and as a result, a PDLC film with high clarity can be obtained.

[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. It is preferable to use a nematic liquid crystal because it 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 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 kinds.

[0040] Specific examples of the dichroic dye include azo dyes, anthraquinone dyes, naphthoquinone dyes, perylene dyes, quinophthalone dyes, tetrazine dyes, and benzothiadiazole dyes. Among them, from the viewpoints of absorption coefficient, solubility in liquid crystal components, light resistance, and the like, it is preferable that the dichroic dye contains anthraquinone dyes or azo dyes. For example, 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 to 196 and 724 to 730 can be used. In addition, 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, and the like.

[0042] The content of the liquid crystal component in the PDLC layer is, for example, 30% by weight to 90% by weight, preferably 35% by weight to 85% by weight, and more preferably 40% by weight 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 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 having high clarity and high colorability can be suitably obtained.

[0047] A-3. Second transparent conductive film The second transparent conductive film 30 typically has a second transparent substrate 32 and a second transparent electrode layer 34 provided on one side (the PDLC layer 20 side) of the second transparent substrate 32. The second transparent conductive film 30 may have a hard coat layer on one or both sides of the second transparent substrate 32, and may also have a refractive index adjustment layer between the second transparent substrate 32 and the second transparent electrode layer 34, as necessary.

[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 further 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 further 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 further 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 manufactured by any suitable manufacturing method. The manufacturing method of the PDLC film described in section A can be, 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 coating layer to obtain a PDLC layer comprising 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 over 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 (hereinafter sometimes referred to as "liquid crystal particles") containing the liquid crystal component and the dichroic dye.

[0054] As the dispersion medium, water or a mixed solvent of water and a water-miscible organic solvent can be preferably used. Examples of the water-miscible organic solvent include C1-3 alcohol, acetone, DMSO, etc. The liquid crystal component and the 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% by weight to 70% by weight, and preferably 40% by weight 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, 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. 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 set to the desired range. The average particle size of the liquid crystal particles means the volume average median size, and can be measured using a dynamic light scattering particle size distribution measuring device.

[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] The liquid crystal emulsion can be prepared by, for example, a mechanical emulsification method, a microchannel method, a membrane emulsification method, etc. Preferably, the liquid crystal emulsion is prepared by a mechanical emulsification method or a membrane emulsification method. According to the mechanical emulsification method, a liquid crystal emulsion having a small particle size can be efficiently obtained. The mechanical emulsification method can be performed using a known dispersion / mixing device such as a homomixer or a homogenizer, and preferably can be performed using a homogenizer such as a high-pressure homogenizer or an ultrasonic homogenizer. In addition, according to the membrane emulsification method, an emulsion having a uniform particle size distribution can be suitably obtained. For details of the membrane emulsification method, the disclosures of JP-A-4-355719, JP-A-2015-40994 (which are incorporated by reference in this specification) and the like can be referred to.

[0060] The order of mixing the liquid crystal component, the dichroic dye, and the dispersion medium is not particularly limited. For example, the liquid crystal component and the dichroic dye may be mixed, and the resulting mixture may be mixed with the dispersion medium, or 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 required. Examples of the optional components include a surfactant, a leveling agent, a crosslinking agent, a dispersion stabilizer, and the like. 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 of the resin dispersion or the solvent of the resin solution may be the same as the dispersion medium used in the preparation of 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 further preferably 50 nm to 200 nm. Two or more kinds of resin particles having different resin types and / or average particle diameters 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 measuring device.

[0064] The particle size of the liquid crystal particles in the coating liquid 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 liquid 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 can 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% by weight to 90% by weight, preferably 35% by weight to 85% by weight, and more preferably 40% by weight 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 for example, 100% by weight or less, preferably 99% by weight or less.

[0068] Examples of the surfactant 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, based on 100 parts by weight of the solid content of the coating liquid.

[0069] 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 is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, relative to 100 parts by weight of the solid content of the coating liquid.

[0070] Examples of the crosslinking agent include aziridine-based crosslinking agents, isocyanate-based crosslinking agents, 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 solids concentration of the coating liquid may 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, and the thickness of the PDLC layer may become unstable. If the viscosity exceeds 400 mPas, the bead of the coating liquid may become unstable. The viscosity of the coating liquid can be measured, for example, by a rheometer MCR302 manufactured by Anton Paar. The viscosity used here is the shear viscosity value under the conditions of 20°C and a shear rate of 1000 (1 / s).

[0075] Any appropriate method can be adopted 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 preferable. For example, the description of JP-A-2019-5698 can be referred to for coating by the roll coating method using a slot die.

[0076] The thickness of the coating layer is preferably from 1 μm to 100 μm, more preferably from 2 μm to 90 μm, and further preferably from 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 the liquid crystal component 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 component, 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., and more preferably 25° C. to 80° C. The drying time is preferably 1 minute to 100 minutes, and 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 on the PDLC layer so that the second transparent electrode layer faces the PDLC layer. From the viewpoint of obtaining 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. EXAMPLES

[0082] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring the various properties are as follows. In addition, unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight.

[0083] (1) Thickness The measurement was performed 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 confirming on the device monitor that the concentration was measurable. (3) Average particle size of resin particles A few drops of the resin dispersion were added to 100 mL of water to prepare a measurement sample. 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 the device monitor was used to confirm that the concentration was measurable, after which the measurement was performed. (4) Hayes The haze was measured according to JIS K 7136 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH4000"). (5) Total light transmittance The measurement was carried out according to 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 cooling 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 a cross-sectional SEM image. The Heywood diameter was calculated from the cross-sectional area of ​​all liquid crystal droplets in a 30 μm × 20 μm area in the cross-sectional SEM image, and 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 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) 27.9 parts, dichroic dye (Hayashibara Corporation, product name "G-470") 0.26 parts, dichroic dye (Hayashibara Corporation, product name "NKX-3739") 0.53 parts, dichroic dye (Hayashibara Corporation, product name "NKX-3708") 1.31 parts, pure water 67 parts, and surfactant (Daiichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") 3 parts were mixed and treated with a high-pressure homogenizer to prepare a liquid crystal emulsion. The average particle size of the liquid crystal particles in the obtained liquid crystal emulsion was 170 nm.

[0086] (Preparation of Coating Fluid) An emulsion coating liquid (solid concentration: 30 wt%) was obtained by mixing 47.6 parts of the above liquid crystal emulsion, 32 parts of a polyether-based polyurethane resin aqueous dispersion (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] (Preparation 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 PDLC layer with a thickness of 16 μm. Then, a second transparent conductive film was laminated on the PDLC layer with the ITO layer facing the PDLC layer while applying a lamination pressure of 0.4 MPa / m using a laminator. 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 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 constant 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, product name "JC-5174XX"), 0.26 parts of dichroic dye (Hayashibara, product name "G-470"), 0.53 parts of dichroic dye (Hayashibara, product name "NKX-3739"), 1.31 parts of dichroic dye (Hayashibara, product name "NKX-3708"), 67 parts of pure water, and 3 parts of surfactant (Daiichi Kogyo Seiyaku, "Noigen ET159") were mixed and roughly dispersed by stirring at 100 rpm for 10 minutes with a homogenizer. The crude dispersion was passed through a separation membrane with a uniform particle size distribution (SPG Techno, "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 operation was repeated 10 times. The volume average particle size of the liquid crystal particles in the obtained liquid crystal emulsion was 2.1 μm.

[0091] (Preparation of Coating Fluid) An emulsion coating liquid (solid concentration: 30 wt%) was obtained by mixing 47.6 parts of the above liquid crystal emulsion, 32 parts of a polyether-based polyurethane resin aqueous dispersion (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] (Preparation 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 PDLC layer with a thickness of 16 μm. Then, a second transparent conductive film was laminated on the PDLC layer with the ITO layer facing the PDLC layer while applying a lamination pressure of 0.4 MPa / m using a laminator. 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 according to the following criteria based on the visibility of the characters when plain paper with characters printed in black ink was visually observed 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 about 200 mm, and the distance from the observer's eye to the plain paper was 200 mm. The evaluation results are shown in Table 1 together with the clarity, total light transmittance, and haze of each PDLC film. Evaluation Criteria Excellent: Very high transparency, allowing characters to be clearly read. Good: Transparency is somewhat high and text is visible. Poor: The transparency is low and the characters 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 suitably used for 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, A polymer dispersed liquid crystal film having a clarity of 90 or more in a colored state.

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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