Polymer-dispersed liquid crystal film, method for producing polymer-dispersed liquid crystal film, and composition for forming polymer-dispersed liquid crystal

Abstract

To provide a PDLC film with highly homogeneous optical properties, and a method of manufacturing the same.SOLUTION: A polymer-dispersed liquid crystal film is provided, comprising a first transparent conductive film, a polymer-dispersed liquid crystal layer containing a polymer matrix and droplets of a liquid crystal compound dispersed in the polymer matrix, and a second transparent conductive film arranged in the described order, the polymer-dispersed liquid crystal layer containing a polymer surfactant having a number-average molecular weight of 9000 g / mol or greater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polymer-dispersed liquid crystal film, a method for producing the polymer-dispersed liquid crystal film, and a composition for forming a polymer-dispersed liquid crystal.

Background Art

[0002] A PDLC film having a polymer-dispersed liquid crystal (Polymer Dispersed Liquid Crystal; hereinafter sometimes referred to as "PDLC") layer between a pair of transparent electrode layers can change the degree of light scattering of transmitted light in the PDLC layer according to the amount of voltage applied. For example, by switching between a voltage-applied state and a non-applied state, a state in which light is scattered (scattering state) and a state in which light is transmitted (non-scattering state or transparent state) can be switched (Patent Document 1). Specifically, the PDLC layer includes a polymer matrix and droplets of a liquid crystal compound (liquid crystal droplets) dispersed in the polymer matrix, and due to the refractive index difference between the liquid crystal compound in the liquid crystal droplets and the polymer matrix, the liquid crystal droplets can become scattering particles and cause light scattering.

[0003] The optical properties such as haze of the above PDLC film can change depending on the thickness of the PDLC layer, the refractive index or blending ratio of the polymer matrix and the liquid crystal compound, the particle diameter of the liquid crystal droplets, etc. Therefore, in order to obtain a PDLC film having desired optical properties, it is desirable to strictly control these factors.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the production of conventional PDLC films, even when produced under the same conditions, variations in the optical properties of the resulting PDLC films sometimes occurred.

[0006] The present invention has been made to solve the above problems, and its main object is to provide a PDLC film having excellent uniformity in optical properties and a method for producing the same.

Means for Solving the Problems

[0007] According to one aspect of the present invention, there is provided a polymer-dispersed liquid crystal film including, in this order, a first transparent conductive film, a polymer-dispersed liquid crystal layer including a polymer matrix and droplets of a liquid crystal compound dispersed in the polymer matrix, and a second transparent conductive film, wherein the polymer-dispersed liquid crystal layer contains a polymer surfactant having a number average molecular weight of 9000 g / mol or more. In one embodiment, the content of the polymer surfactant in the polymer-dispersed liquid crystal layer is 0.2 parts by weight to 4.2 parts by weight with respect to 100 parts by weight of the liquid crystal compound. In one embodiment, the polymer surfactant is a nonionic polymer surfactant. According to another aspect of the present invention, there is provided a method for producing a polymer-dispersed liquid crystal film including: mixing a liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, and a dispersion medium to prepare a liquid crystal emulsion containing particles of the liquid crystal compound; mixing the liquid crystal emulsion and a resin for forming a polymer matrix to prepare a coating liquid containing particles of the liquid crystal compound; coating the coating liquid on a first transparent conductive film to obtain a coated layer; drying the coated layer to obtain a polymer-dispersed liquid crystal layer including a polymer matrix and droplets of the liquid crystal compound dispersed in the polymer matrix; and laminating a second transparent conductive film on the polymer-dispersed liquid crystal layer. In one embodiment, the content of the polymer surfactant in the coating liquid is 0.2 parts by weight to 4.2 parts by weight with respect to 100 parts by weight of the liquid crystal compound. In one embodiment, the polymer surfactant is a nonionic polymer surfactant. According to another aspect of the present invention, a liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, a resin for forming a polymer matrix, and a dispersion medium are included, and particles of the liquid crystal compound are dispersed in the dispersion medium. In one embodiment, the content of the polymer surfactant is 0.2 parts by weight to 4.2 parts by weight with respect to 100 parts by weight of the liquid crystal compound. In one embodiment, the polymer surfactant is a nonionic polymer surfactant. In one embodiment, the average particle diameter of the particles of the liquid crystal compound is 2.5 μm to 3.5 μm. In one embodiment, the change rate of the average particle diameter of the particles of the liquid crystal compound defined by the following formula is 30% or less. Change rate of average particle diameter of liquid crystal compound particles (%) = (Average particle diameter of liquid crystal compound particles 72 hours after preparation - Average particle diameter of liquid crystal compound particles immediately after preparation) / Average particle diameter of liquid crystal compound particles immediately after preparation × 100

Advantages of the Invention

[0008] According to an embodiment of the present invention, by manufacturing a PDLC film using a PDLC-forming composition containing a liquid crystal compound, a polymer surfactant, a resin for forming a polymer matrix, and a dispersion medium, and in which particles of the liquid crystal compound are dispersed in the dispersion medium, a PDLC film excellent in optical property uniformity can be obtained. The reason for this effect is not intended to limit the present invention in any way, but can be presumed as follows. That is, in the production of conventional PDLC films, the particle diameter of the liquid crystal compound particles in the PDLC-forming composition changes over time, which contributes to variations in the optical properties of the resulting PDLC film. In contrast, by blending a polymer surfactant into the PDLC-forming composition, it is presumed that the change in the particle diameter of the liquid crystal compound particles can be suppressed, and as a result, a PDLC film excellent in optical property uniformity can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3

Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments. In this specification, "~" representing a numerical range includes the numerical values of its upper and lower limits.

[0011] A. Polymer-dispersed liquid crystal film According to one aspect of the present invention, there is provided a polymer-dispersed liquid crystal film including, in this order, a first transparent conductive film, a polymer-dispersed liquid crystal layer including a polymer matrix and droplets of a liquid crystal compound dispersed in the polymer matrix, and a second transparent conductive film, wherein the polymer-dispersed liquid crystal layer contains a polymer surfactant having a number average molecular weight of 9000 g / mol or more.

[0012] FIG. 1 is a schematic cross-sectional view of a PDLC film according to one embodiment of the present invention. The PDLC film 100 includes, in this order, a first transparent conductive film 10, a PDLC layer 20 including a polymer matrix 22 and liquid crystal droplets 24 dispersed in the polymer matrix 22, and a second transparent conductive film 30. Although not shown, an alignment film may be provided, if necessary, on the surfaces of the first transparent conductive film 10 and the second transparent conductive film 30 that are in contact with the PDLC layer 20.

[0013] As described above, the degree of scattering of transmitted light (and as a result, haze) of the PDLC film changes according to the applied voltage. In one embodiment, the PDLC film is in a transparent state when a voltage is applied and has a lower haze than when no voltage is applied (normal mode). In another embodiment, the PDLC film is in a scattered state when a voltage is applied and has a higher haze than when no voltage is applied (reverse mode).

[0014] According to the normal-mode PDLC film, when no voltage is applied, the liquid crystal compounds in the PDLC layer are not aligned, resulting in a scattered state. When a voltage is applied, the liquid crystal compounds are aligned, and as a result, the refractive index of the liquid crystal compounds and the refractive index of the polymer matrix are aligned, enabling a transparent state to be achieved.

[0015] According to the reverse-mode PDLC film, the liquid crystal compounds in the PDLC layer are aligned by the alignment film provided on the surface of the transparent conductive film to be in a transparent state when no voltage is applied, and the alignment of the liquid crystal compounds can be disrupted by the application of a voltage to be in a scattered state.

[0016] The haze of the PDLC film in the transparent state can preferably be 50% or less, more preferably 35% or less. Also, the haze of the PDLC film in the scattered state can preferably be 60.0% to 99.9%, more preferably 65.0% to 99.8%, and even more preferably 70.0% to 99.7%.

[0017] The total light transmittance of the PDLC film in the transparent state can preferably be 40% to 99%, more preferably 50% to 95%. Also, the total light transmittance of the PDLC film in the scattered state can preferably be 5% to 65%, more preferably 10% to 60%. The total light transmittance can be measured in accordance with JIS K 7361.

[0018] The voltage applied to the PDLC film during voltage application is a voltage (operating voltage) capable of operating the PDLC film, and can be, for example, 5V to 200V, preferably 10V to 100V. In this specification, "haze at the time of voltage application" means the haze when an operating voltage is applied to the PDLC film, and can be, for example, the haze when a voltage of 5V or more, 10V or more, or 20V or more is applied.

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

[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 thereof (the PDLC layer 20 side). The first transparent conductive film 10 may have a hard coat layer on one or both sides of the first transparent substrate 12 as needed, and may also have a refractive index adjustment 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 1Ω / □ to 1000Ω / □, more preferably 5Ω / □ to 300Ω / □, and even more preferably 10Ω / □ to 200Ω / □.

[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 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; cellulose resins, etc. Among them, polyester resins, cycloolefin resins or acrylic resins are preferably used. These resins are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, etc. The above thermoplastic resins may be used alone or in combination of two or more. Also, it is possible to use an optical film such as a retardation film, a high retardation substrate, a retardation plate, an absorption type polarizing film, a polarization selective reflection film, etc. as the first transparent substrate as used in a polarizing plate.

[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 exerted.

[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, for example, metal oxides such as indium tin oxide (ITO), zinc oxide (ZnO), tin oxide (SnO2), etc. Preferably, a transparent electrode layer containing ITO is formed. The transparent electrode layer containing ITO is excellent in transparency. The first transparent electrode layer can be patterned into a desired shape according to the purpose.

[0028] The 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 light transmittance in such a range, a PDLC film having a high light transmittance in the transparent state can be obtained. The higher the light transmittance, the more preferable it is, and the upper limit thereof is, for example, 99%.

[0029] Preferably, the first transparent electrode layer contains crystal grains. By containing crystal grains, the light transmittance can be improved. There is no limitation on the method of forming crystal grains. For example, crystal grains can be preferably formed by heating the transparent electrode layer in the atmosphere. The area occupancy rate of crystal grains in the transparent electrode layer is, for example, 30% or more, preferably 50% or more, more preferably 80% or more. The upper limit of the area occupancy rate is, for example, 100%. If the area occupancy rate of crystal grains is within the above range, the light transmittance can be improved. Incidentally, the area occupancy rate of crystal grains can be calculated from the area ratio of the crystal grain region and the amorphous region by observing the surface of the transparent electrode layer with a transmission electron microscope (TEM).

[0030] The surface roughness Ra of the first transparent electrode layer is, for example, 0.1 nm or more. When the surface roughness Ra of the first transparent electrode layer is less than 0.1 nm, the adhesion to the first transparent substrate may deteriorate. The upper limit of the surface roughness Ra of the first transparent electrode layer is preferably less than 1.2 nm, more preferably 1.0 nm or less, still more preferably less than 1.0 nm, and particularly preferably 0.8 nm or less. When the surface roughness Ra of the first transparent electrode layer is too large, it may be difficult to preferably form crystal grains. Incidentally, the surface roughness Ra in this specification means the arithmetic mean roughness Ra measured by an AFM (Atomic Force Microscope).

[0031] The thickness of the first transparent electrode layer is, for example, 10 nm or more, preferably 15 nm or more. When the thickness of the transparent electrode layer is less than 10 nm, the area occupancy rate of crystal grains may decrease. The upper limit of the thickness of the first transparent electrode layer is, for example, 50 nm or less, preferably 35 nm or less, more preferably less than 30 nm, and still more preferably 27 nm or less. When the thickness of the transparent electrode layer exceeds 50 nm, the transmittance may deteriorate, and the surface roughness of the transparent electrode layer may increase.

[0032] The first transparent electrode layer is provided on one surface of the first transparent substrate, for example, by sputtering. After forming a metal oxide layer by sputtering, it can be crystallized by annealing. The annealing is performed, for example, by heat treatment at 120°C to 300°C for 10 minutes to 120 minutes.

[0033] Regarding the refractive index adjustment layer and the hard coat layer, a configuration well-known in the art can be adopted, so the detailed description thereof is omitted.

[0034] A-2. Polymer-dispersed liquid crystal layer The PDLC layer 20 includes a polymer matrix 22 and droplets (liquid crystal droplets) 24 of a liquid crystal compound dispersed in the polymer matrix 22. The polymer-dispersed liquid crystal layer further includes a polymer surfactant having a number average molecular weight of 9000 g / mol or more.

[0035] The average particle diameter of the liquid crystal droplets can be, for example, 0.3 μm to 9 μm, preferably 0.4 μm to 8 μm. If the average particle diameter of the liquid crystal droplets is too small, since the liquid crystal droplet size is smaller than the wavelength of light, light will pass through the liquid crystal droplets without scattering, and as a result, the problem that sufficient haze cannot be obtained may occur. Also, if the average particle diameter is too large, since the liquid crystal droplet size is too large compared to the wavelength of light, the problem that sufficient haze cannot be obtained may occur. Note that the average particle diameter of the liquid crystal droplets in the PDLC layer is the volume average particle diameter of the liquid crystal droplets when viewed from a direction perpendicular to the main surface of the PDLC film.

[0036] The particle diameter of the liquid crystal droplets preferably has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the particle diameter of the liquid crystal droplets can be, for example, less than 0.4, preferably 0.35 or less, more preferably 0.3 or less.

[0037] Incidentally, the average particle diameter and the coefficient of variation (CV value) of the particle diameter of the liquid crystal droplets in the PDLC layer can be measured, for example, as follows. That is, after peeling off the second transparent conductive film of the PDLC film to expose the PDLC layer, the surface of the exposed PDLC layer is observed with a transmission optical microscope at a magnification of 100 times the objective lens and a field of view of 100 μm square. While gradually changing the focus, the particle diameter is measured in 0.1 μm units at the focus position where the focus is most suitable for each liquid crystal droplet, and the volume average particle diameter is obtained by performing statistical processing based on volume. The coefficient of variation (CV value) calculated below can be calculated. CV value = standard deviation of the particle distribution based on volume / volume average particle diameter

[0038] The polymer matrix can be composed of any suitable resin. The resin for forming the polymer matrix can be appropriately selected according to the light transmittance, the refractive index of the liquid crystal compound, the adhesion to the transparent conductive film, etc. For example, water-soluble resins or water-dispersible resins such as urethane resins, polyvinyl alcohol resins, polyethylene resins, polypropylene resins, and acrylic resins can be preferably used. The resin for forming the polymer matrix may be used alone or in combination of two or more.

[0039] As the liquid crystal compound, any suitable liquid crystal compound can be used. Preferably, it has a birefringence Δn of 0.05 to 0.50 at a wavelength of 589 nm (= ne - no; ne is the refractive index in the long axis direction of the liquid crystal compound molecule, no is the refractive index in the short axis direction of the liquid crystal compound molecule), and more preferably a birefringence Δn of 0.10 to 0.45. The liquid crystal compound may be used alone or in combination of two or more.

[0040] The dielectric anisotropy of the liquid crystal compound may be positive or negative. The liquid crystal compound can be, for example, a nematic, smectic, or cholesteric liquid crystal compound. Since excellent transparency can be realized in the transparent state, it is preferable to use a nematic liquid crystal compound.

[0041] Examples of nematic liquid crystal compounds include biphenyl compounds, phenyl benzoate compounds, cyclohexylbenzene compounds, azoxybenzene compounds, azobenzene compounds, azomethine compounds, terphenyl compounds, biphenyl benzoate compounds, cyclohexyl biphenyl compounds, phenyl pyridine compounds, cyclohexyl pyrimidine compounds, cholesterol compounds, fluorine compounds, and the like.

[0042] As the polymer surfactant, any suitable surfactant having a number average molecular weight of 9000 g / mol or more can be used. The number average molecular weight of the polymer surfactant is preferably from 10000 g / mol to 500000 g / mol, more preferably from 10000 g / mol to 100000 g / mol. By using a surfactant having a number average molecular weight within this range, a PDLC film having desired optical properties can be stably produced. The number average molecular weight is a value determined in terms of styrene by GPC analysis.

[0043] The HLB value of the polymer surfactant can be, for example, 12 or more, preferably 13 or more, more preferably 14 or more. The HLB value can be, for example, 17 or less, or for example 16 or less.

[0044] Specific examples of the polymer surfactant include nonionic polymer surfactants such as polyoxyalkylene copolymers (copolymers of two or more oxyalkylenes), polyvinyl alcohol, polyvinyl pyrrolidone, poly(meth)acrylamide, and higher alcohols; anionic polymer surfactants such as poly(meth)acrylic acid and its copolymers (e.g., styrene-(meth)acrylic acid copolymer, vinyl naphthalene-(meth)acrylic acid copolymer), polymaleic acid and its copolymers (e.g., styrene-maleic acid copolymer, vinyl naphthalene-maleic acid copolymer), and polyphosphoric acid; and cationic polymer surfactants such as dimethylaminoethyl (poly)methacrylate, diethylaminoethyl (poly)methacrylate, and dimethylaminopropyl (poly)methacrylate. The polymer surfactant may be used alone or in combination of two or more.

[0045] As the polymer surfactant, a nonionic surfactant is preferred, and a polyoxyalkylene copolymer is more preferred. Specific examples of the polyoxyalkylene copolymer include block copolymers of polyoxyethylene and polyoxypropylene, and copolymers having a triblock structure of polyoxyethylene-polyoxypropylene-polyoxyethylene (so-called Pluronic (registered trademark) surfactants) can be preferably exemplified. Commercially available products of Pluronic surfactants include the Newpol series (PE-68, 78, 108, 128, etc.) manufactured by Sanyo Chemical Industries, Ltd.

[0046] The PDLC layer may further contain any appropriate component as necessary. Such optional components include surfactants other than the above polymer surfactant, leveling agents, crosslinking agents, dispersion stabilizers, and the like.

[0047] The content ratio of the liquid crystal compound in the PDLC layer is, for example, 30% by weight to 70% by weight, preferably 35% by weight to 65% by weight, and more preferably 40% by weight to 60% by weight.

[0048] The content of the polymer matrix in the PDLC layer is, for example, 50 to 230 parts by weight, preferably 60 to 200 parts by weight, more preferably 80 to 120 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

[0049] The content of the polymer surfactant in the PDLC layer is, for example, 0.2 to 4.2 parts by weight, preferably 0.5 to 3.0 parts by weight, more preferably 0.8 to 2.1 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

[0050] The total content ratio of the polymer matrix, the liquid crystal compound, and the polymer surfactant in the PDLC layer is, for example, 90% by weight or more, preferably 95% by weight or more, and for example, 100% by weight or less, preferably 99% by weight or less.

[0051] The thickness of the PDLC layer is typically 2 to 40 μm, preferably 3 to 35 μm, more preferably 4 to 30 μm.

[0052] A-3. The 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 thereof (the PDLC layer 20 side). The second transparent conductive film 30 may have a hard coat layer on one or both sides of the second transparent substrate 32 as required, and may also have a refractive index adjustment layer between the second transparent substrate 32 and the second transparent electrode layer 34.

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

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

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

[0056] Regarding the second transparent substrate and the second transparent electrode layer, the same explanations as those for the first transparent substrate and the first transparent electrode layer can be respectively applied. The second transparent conductive film may have the same configuration as the first transparent conductive film or a different configuration.

[0057] B. Method for manufacturing a polymer-dispersed liquid crystal film According to another aspect of the present invention, mixing a liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, and a dispersion medium to prepare a liquid crystal emulsion containing particles of the liquid crystal compound (Step A), mixing the liquid crystal emulsion and a resin for forming a polymer matrix to prepare a coating liquid containing particles of the liquid crystal compound (Step B), coating the first transparent conductive film with the coating liquid to obtain a coating layer (Step C), drying the coating layer to obtain a polymer-dispersed liquid crystal layer containing a polymer matrix and droplets of the liquid crystal compound dispersed in the polymer matrix (Step D), and laminating a second transparent conductive film on the polymer-dispersed liquid crystal layer (Step E), A method for manufacturing a polymer-dispersed liquid crystal film is provided, which includes the above steps.

[0058] B-1. Step A In Step A, a liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, and a dispersion medium are mixed to prepare a liquid crystal emulsion containing particles of the liquid crystal compound.

[0059] 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 compound and the polymer surfactant are as described in Section A.

[0060] The content ratio of the liquid crystal compound in the liquid crystal emulsion is, for example, 30% by weight to 70% by weight, preferably 40% by weight to 60% by weight.

[0061] The content of the polymer surfactant in the liquid crystal emulsion is, for example, 0.2 parts by weight to 4.2 parts by weight, preferably 0.5 parts by weight to 3.0 parts by weight, more preferably 0.8 parts by weight to 2.1 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

[0062] The average particle diameter of the liquid crystal compound particles in the liquid crystal emulsion is preferably 0.3 μm or more, more preferably 0.4 μm or more. Also, the average particle diameter of the liquid crystal compound particles is preferably 9 μm or less, more preferably 8 μm or less. In one embodiment, the average particle diameter of the liquid crystal compound particles in the liquid crystal emulsion can be, for example, 2.0 μm to 5.0 μm, or for example 2.0 μm to 4.0 μm, or for example 2.5 μm to 3.5 μm. The particle diameter of the liquid crystal droplets in the PDLC layer can usually be determined by the particle diameter of the liquid crystal compound particles in the liquid crystal emulsion. Therefore, if the average particle diameter of the liquid crystal compound particles in the liquid crystal emulsion is within the above range, the average particle diameter of the liquid crystal droplets in the PDLC layer can be made within the above desired range. Further, according to the embodiment of the present invention, by the presence of the bulky polymer surfactant surrounding the surface of the liquid crystal compound particles, contact and coalescence of the liquid crystal compound particles with each other in the liquid crystal emulsion or in the coating liquid described later can be prevented, and the temporal stability of the particle diameter of the liquid crystal compound particles can be improved. Note that the average particle diameter of the above liquid crystal compound particles is the volume average particle diameter.

[0063] The particle diameter of the liquid crystal compound particles preferably has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the particle diameter of the liquid crystal compound particles can be, for example, less than 0.4, preferably 0.35 or less, more preferably 0.3 or less.

[0064] The liquid crystal emulsion can be prepared, for example, by a mechanical emulsification method, a microchannel method, a membrane emulsification method, or the like. Preferably, the liquid crystal emulsion is prepared by the membrane emulsification method. According to the membrane emulsification method, an emulsion with a uniform particle size distribution can be preferably obtained. For details of the membrane emulsification method, reference can be made to the disclosures of JP-A-4-355719, JP-A-2015-40994 (these are incorporated herein by reference), and the like.

[0065] B-2. Step B In Step B, the liquid crystal emulsion obtained in Step A and the resin for forming the polymer matrix are mixed to prepare a coating liquid containing particles of the liquid crystal compound. The coating liquid may contain any other components as necessary. Examples of the optional components include surfactants other than polymer surfactants, leveling agents, crosslinking agents, dispersion stabilizers, and the like. These optional components may be added during the preparation of the liquid crystal emulsion in Step A depending on the purpose.

[0066] The resin for forming the polymer matrix is as described in Item A. The polymer matrix resin is mixed with the liquid crystal emulsion, for example, as a resin dispersion in which resin particles for forming the polymer matrix are dispersed in a dispersion medium or as a resin solution in which the resin for forming the polymer matrix is dissolved in a solvent. At this time, the same substances as the dispersion medium used in the preparation of the liquid crystal emulsion can be used as the dispersion medium of the resin dispersion or the solvent of the resin solution.

[0067] The average particle diameter of the resin particles for forming the 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 having different resin types and / or average particle diameters may be used. The average particle diameter of the resin particles for forming the polymer matrix means the volume-average median diameter and can be measured using a dynamic light scattering particle size distribution measuring device.

[0068] The particle size of the liquid crystal compound 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 compound particles in the coating liquid is preferably 0.3 μm or more, more preferably 0.4 μm or more. Also, the average particle size of the liquid crystal compound particles is preferably 9 μm or less, more preferably 8 μm or less. In one embodiment, the average particle size of the liquid crystal compound particles in the coating liquid can be, for example, 2.0 μm to 5.0 μm, or for example, 2.0 μm to 4.0 μm, or for example, 2.5 μm to 3.5 μm.

[0069] The content ratio of the liquid crystal compound in the solid content of the coating liquid can be, for example, 30% by weight to 70% by weight, preferably 35% by weight to 65% by weight, more preferably 40% by weight to 60% by weight.

[0070] The content of the resin for forming the polymer matrix in the solid content of the coating liquid is, for example, 50 parts by weight to 230 parts by weight, preferably 60 parts by weight to 200 parts by weight, more preferably 80 parts by weight to 120 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

[0071] The content of the polymer surfactant in the solid content of the coating liquid is, for example, 0.2 parts by weight to 4.2 parts by weight, preferably 0.5 parts by weight to 3.0 parts by weight, more preferably 0.8 parts by weight to 2.1 parts by weight with respect to 100 parts by weight of the liquid crystal compound. Examples of surfactants other than the polymer surfactant include, for example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, etc. The content ratio of surfactants other than the polymer surfactant is preferably 0.2 parts by weight to 4.2 parts by weight, more preferably 0.8 parts by weight to 2.1 parts by weight with respect to 100 parts by weight of the coating liquid.

[0072] Examples of the leveling agent include, for example, acrylic leveling agents, fluorine-based leveling agents, silicone-based leveling agents, etc. The content ratio of the leveling agent is preferably 0.05 parts by weight to 10 parts by weight, more preferably 0.1 parts by weight to 1 part by weight with respect to 100 parts by weight of the coating liquid.

[0073] Examples of the crosslinking agent include aziridine-based crosslinking agents and isocyanate-based crosslinking agents. The content ratio of the crosslinking agent is preferably 0.5 parts by weight to 10 parts by weight, more preferably 0.8 parts by weight to 5 parts by weight, based on 100 parts by weight of the coating liquid.

[0074] The solid content concentration of the coating liquid can be, for example, 20% by weight to 60% by weight, preferably 30% by weight to 50% by weight.

[0075] The coating liquid prepared in Item B is a composition for forming a polymer-dispersed liquid crystal. The composition for forming a polymer-dispersed liquid crystal contains a liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, a resin for forming a polymer matrix, and a dispersion medium, and the particles of the liquid crystal compound are dispersed in the dispersion medium.

[0076] In one embodiment, the change rate of the average particle diameter of the liquid crystal compound particles in the coating liquid defined by the following formula (1) is preferably 30% or less, more preferably 10% or less. The "average particle diameter of the liquid crystal compound particles immediately after preparation" in formula (1) can be the average particle diameter of the liquid crystal compound particles in the coating liquid measured at any timing within 60 minutes after preparation. Change rate of average particle diameter of liquid crystal compound particles (%) = (Average particle diameter of liquid crystal compound particles 72 hours after preparation - Average particle diameter of liquid crystal compound particles immediately after preparation) / Average particle diameter of liquid crystal compound particles immediately after preparation × 100 (1)

[0077] B-3. Step C In Step C, the coating liquid prepared in Item B is applied to the first transparent conductive film to obtain a coating layer.

[0078] Typically, the coating liquid is applied to the surface on the transparent electrode layer side of the first transparent conductive film. The first transparent conductive film is as described in Item A.

[0079] The viscosity of the coating liquid during coating is preferably 20 mPas to 400 mPas, more preferably 30 mPas to 300 mPas, and even more preferably 40 mPas to 200 mPas. When the viscosity is less than 20 mPas, the convection of the dispersion medium becomes significant when drying the dispersion medium, and the thickness of the PDLC layer may become unstable. Also, when the viscosity exceeds 400 mPas, the beads of the coating liquid may not be stable. The viscosity of the coating liquid can be measured, for example, by a rheometer MCR302 manufactured by Anton Paar. The viscosity here uses the value of the shear viscosity under the conditions of 20 °C and a shear rate of 1000 (1 / s).

[0080] As the coating method, any appropriate method can be adopted. For example, roll coating method, spin coating method, bar coating method, dip coating method, die coating method, curtain coating method, spray coating method, knife coating method (comma coating method, etc.) and the like can be mentioned. Among them, the roll coating method is preferred. For example, regarding the coating by the roll coating method using a slot die, reference can be made to the description in JP-A-2019-5698.

[0081] The thickness of the coating layer is preferably 5 μm to 100 μm, more preferably 7.5 μm to 90 μm, and even more preferably 10 μm to 75 μm. Within such a range, a PDLC layer excellent in thickness uniformity can be obtained.

[0082] B-4. Step D In Step D, the coating layer is dried to obtain a PDLC layer containing a polymer matrix and droplets of a liquid crystal compound dispersed in the polymer matrix. As a result of removing the dispersion medium from the coating layer by drying, the resin for forming the polymer matrix and the liquid crystal compound particles remain, and a PDLC layer having a structure in which liquid crystal droplets are dispersed in the polymer matrix is formed.

[0083] The drying of the coating layer can be carried out by any suitable method. Specific examples of the drying method include heat drying, hot air drying, and the like. When the coating liquid contains a crosslinking agent, a crosslinked structure of the polymer matrix can be formed during drying.

[0084] 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.

[0085] B-5. Step E In Step E, a second transparent conductive film is laminated on the PDLC layer. Thereby, a PDLC film having the first transparent conductive film, the PDLC layer, and the second transparent conductive film in this order is obtained.

[0086] Regarding the second conductive film, it is as described in Item A. The lamination of the second transparent conductive film on the PDLC layer is performed such that the second transparent electrode layer side faces the PDLC layer. From the viewpoint of obtaining sufficient adhesion, this lamination can preferably be carried out 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

[0087] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples in any way. The measurement methods for each property are as follows. Also, unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight.

[0088] (1) Thickness It was measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). (2) Volume average particle diameter and particle size distribution of liquid crystal compound particles in the liquid crystal emulsion and the coating liquid Using a dynamic light scattering particle size distribution measuring device (manufactured by Microtrac, model name "MT3300"), 0.02 mL of the measurement sample was set in the measurement holder of the device, and after confirming with the device monitor that the concentration was measurable, the measurement was carried out. (3) Haze Using a product named "NDH4000" manufactured by Nippon Denshoku Industries Co., Ltd., the measurement was carried out based on JIS K 7136. (4) Number average molecular weight Regarding the Pluronic surfactant used in Example 1 and Example 2, the number average molecular weight presented by the manufacturing company was adopted. Regarding the nonionic surfactant used in Comparative Example 1, GPC measurement was carried out by the following method, and the number average molecular weight was determined by converting to polystyrene equivalent using a calibration curve with standard polystyrene. · Device: "Agilent 1200" manufactured by Agilent Technology · Detector: Differential refractometer · Column: TSKgel SuperAWM-H + superAW4000 + superAW2500 manufactured by Tosoh Corporation · Mobile phase: DMF · Measurement temperature: 40 °C · Flow rate: 0.4 mL / min · Injection volume: 40 μL

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

[0090] (Preparation of liquid crystal emulsion) 59.7 parts of a liquid crystal compound (manufactured by JNC, product name "JC-5240XX", birefringence Δn = 0.252 (ne = 1.766, no = 1.514), viscosity = 75.0 mPa·s), 39.8 parts of pure water, and 0.5 part of a pluronic surfactant (manufactured by Sanyo Chemical Industries, product name "Newpole PE-108", number average molecular weight: 16,000) were mixed, and a liquid crystal emulsion was prepared using a membrane emulsification device (manufactured by SPD Technology, "Pumping Connector PC-10N"). The average particle diameter of the liquid crystal compound particles in the obtained liquid crystal emulsion was 3.0 μm.

[0091] (Preparation of Coating Liquid) 31.9 parts of the above liquid crystal emulsion, 11.7 parts of an aqueous dispersion of a polyether-based polyurethane resin (manufactured by DSM, trade name "NeoRez R967", solid content: 40 wt%), 31.1 parts of an aqueous dispersion of an acrylic resin (manufactured by DIC, trade name "Barnock WE-314", solid content: 45 wt%), 4.0 parts of a leveling agent (manufactured by DIC, product name "F-444", pre-diluted to 10 wt% solid content), 3.7 parts of a dispersion stabilizer (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "Pitzcole K90L", pre-diluted to 10 wt% solid content), and 2.7 parts of a crosslinking agent (tris[3-(2-methylaziridin-1-yl)propionic acid]=propylidine trimethyl, pre-diluted to 50 wt% solid content), 14.9 parts of pure water were mixed to obtain a coating liquid (solid content concentration: 40 wt%).

[0092] (Fabrication of PDLC Film) Immediately after the preparation of the above coating liquid (within 60 minutes), 24 hours later, 48 hours later, and 72 hours later, PDLC films were fabricated using the above coating liquid. Specifically, the coating liquid was applied to the ITO layer surface of the first transparent conductive film using a non-wire bar (manufactured by OSP Systems Products Co., Ltd., product name "OSP-25-L400"). Next, the coating layer was dried at 25°C for 60 minutes to form a PDLC layer with a thickness of 6.2 μm to 6.5 μm. While applying a lamination pressure of 0.4 MPa / m using a laminator, the second transparent conductive film was laminated on the PDLC layer such that the ITO layer faced the PDLC layer. Thereby, a PDLC film was obtained.

[0093] [Example 2] A PDLC film was prepared in the same manner as in Example 1, except that a Pluronic surfactant (manufactured by Sanyo Chemical Industries, Ltd., product name "Newpole PE-78", number average molecular weight: 9400) was used instead of the Pluronic surfactant (manufactured by Sanyo Chemical Industries, Ltd., product name "Newpole PE-108", number average molecular weight: 16000).

[0094] [Comparative Example 1] A PDLC film was prepared in the same manner as in Example 1, except that a nonionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name "Neugen ET-159", number average molecular weight: 871) was used instead of the Pluronic surfactant (manufactured by Sanyo Chemical Industries, Ltd., product name "Newpole PE-108", number average molecular weight: 16000).

[0095] <Evaluation of Optical Properties of PDLC Film> In the above Examples and Comparative Examples, the haze was measured when an AC voltage of 0 V to 50 V was applied to the PDLC films prepared using the coating liquids immediately after preparation (within 60 minutes), 24 hours later, 48 hours later, and 72 hours later. The results are shown in FIGS. 2A to 2C. In the figures, (b) is an enlarged view of the region where the applied voltage in (a) is 0 V to 15 V.

[0096] <Evaluation of Particle Size of Liquid Crystal Compound Particles in Coating Liquid> The particle size distributions of the liquid crystal compound particles in the coating liquids in the above Examples and Comparative Examples immediately after preparation (within 60 minutes), 24 hours later, 48 hours later, and 72 hours later are shown in FIG. 3. For the coating liquids prepared in Example 1, Example 2, and Comparative Example 1, the change rates of the volume average particle size of the liquid crystal compound particles defined by the above formula (1) were 0.3%, 30.0%, and 70.4%, respectively.

[0097] As shown in FIGS. 2A to 2C, the PDLC film of the example prepared using a surfactant with a large number average molecular weight is excellent in the stability of optical properties regardless of the time from the preparation of the coating liquid to the preparation of the PDLC film. On the other hand, in the PDLC film of the comparative example prepared using a surfactant with a small number average molecular weight, the optical properties change as the time from the preparation of the coating liquid to the preparation of the PDLC film becomes longer (specifically, the haze in the scattered state decreases). As shown in FIG. 3, this is presumably because in the coating liquid prepared using a surfactant with a large number average molecular weight, the temporal stability of the particle diameter of the liquid crystal compound particles is high.

Industrial Applicability

[0098] The PDLC film of the present invention is suitably used for various applications such as displays such as advertisements and guide plates, and smart windows.

Explanation of Symbols

[0099] 100 PDLC film 10 First transparent conductive film 20 PDLC layer 22 Polymer matrix 24 Liquid crystal droplet 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 including a polymer matrix and droplets of a liquid crystal compound dispersed in the polymer matrix, and a second transparent conductive film, wherein the polymer-dispersed liquid crystal layer contains a polymer surfactant having a number average molecular weight of 9000 g / mol or more, and the polymer surfactant is one or more selected from block copolymers of polyoxyethylene and polyoxypropylene, polyvinyl alcohol, polyvinyl pyrrolidone, and poly(meth)acrylamide.

2. The polymer-dispersed liquid crystal film according to claim 1, wherein the content of the polymer surfactant in the polymer-dispersed liquid crystal layer is 0.2 parts by weight to 4.2 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

3. Preparing a liquid crystal emulsion containing particles of the liquid crystal compound by mixing the liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, and a dispersion medium, preparing a coating liquid containing particles of the liquid crystal compound by mixing the liquid crystal emulsion and a resin for forming a polymer matrix, coating the coating liquid on the first transparent conductive film to obtain a coated layer, drying the coated layer to obtain a polymer-dispersed liquid crystal layer including a polymer matrix and droplets of the liquid crystal compound dispersed in the polymer matrix, and laminating a second transparent conductive film on the polymer-dispersed liquid crystal layer. A method for manufacturing a polymer-dispersed liquid crystal film, comprising the above steps.

4. The manufacturing method according to claim 3, wherein the content of the polymer surfactant in the coating liquid is 0.2 parts by weight to 4.2 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

5. The manufacturing method according to claim 3 or 4, wherein the polymer surfactant is a nonionic polymer surfactant.

6. A composition for forming a polymer-dispersed liquid crystal, comprising a liquid crystal compound, a polymer surfactant having a number average molecular weight of 9000 g / mol or more, a resin for forming a polymer matrix, and a dispersion medium, wherein particles of the liquid crystal compound are dispersed in the dispersion medium.

7. The composition for forming a polymer-dispersed liquid crystal according to claim 6, wherein the content of the polymer surfactant is 0.2 parts by weight to 4.2 parts by weight with respect to 100 parts by weight of the liquid crystal compound.

8. The composition for forming a polymer-dispersed liquid crystal according to claim 6 or 7, wherein the polymer surfactant is a nonionic polymer surfactant.

9. The polymer-dispersed liquid crystal-forming composition according to any one of claims 6 to 8, wherein the average particle diameter of the particles of the liquid crystal compound is 2.5 μm to 3.5 μm.

10. The polymer-dispersed liquid crystal-forming composition according to any one of claims 6 to 9, wherein the change rate of the average particle diameter of the particles of the liquid crystal compound defined by the following formula is 30% or less. Change rate of average particle diameter of particles of liquid crystal compound (%) = (Average particle diameter of particles of liquid crystal compound 72 hours after preparation) - (Average particle diameter of particles of liquid crystal compound immediately after preparation) / (Average particle diameter of particles of liquid crystal compound immediately after preparation) × 100

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