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

Abstract

The present application can provide a PDLC layer having excellent uniformity in thickness, and a PDLC film in which leakage of liquid crystal from the PDLC layer is suppressed. The method for producing a polymer-dispersed liquid crystal film of the present application includes: forming a coating layer on a first transparent conductive film by applying an emulsion on the first transparent conductive film, the emulsion being an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent; drying the coating layer to form a polymer-dispersed liquid crystal layer, the polymer-dispersed liquid crystal layer including a polymer matrix and liquid crystal particles dispersed in the polymer matrix; and laminating a second transparent conductive film on the polymer-dispersed liquid crystal layer, wherein the polymer particles include first polymer particles and second polymer particles, the average particle diameter of the second polymer particles being larger than the average particle diameter of the first polymer particles.

Description

Technical Field

[0001] The present invention relates to an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent, a method for manufacturing a polymer-dispersed liquid crystal film using the emulsion, and a polymer-dispersed liquid crystal film obtained using the emulsion. Background Technology

[0002] A PDLC film, which has a polymer-dispersed liquid crystal (PDLC) layer between a pair of transparent electrode layers, can change the degree of scattering of transmitted light in the PDLC layer according to the amount of voltage applied. For example, by switching between the voltage-applied state and the non-applied state, the state of light scattering (scattering state) and the state of light transmission (non-scattering state or transparent state) can be switched. In recent years, the function of such PDLC films has been utilized in various applications such as blinds or curtains, displays, and projection screens.

[0003] As a method for manufacturing PDLC films, the following method is known in the past: after filling a mixture of monomer and liquid crystal compound between a pair of transparent conductive films, the monomer is polymerized by UV irradiation or the like, resulting in polymerization-induced phase separation, thereby forming a PDLC layer in which liquid crystal compound is dispersed in a polymer matrix (for example, Patent Document 1).

[0004] Here, the light diffusion of the PDLC film is proportional to the thickness of the PDLC layer; therefore, uneven PDLC layer thickness leads to uneven display quality. Thus, the uniformity of the PDLC layer thickness is crucial, especially in display applications. However, distortions in the roundness of the laminating rollers or slight misalignments of the roller core during the filling of the mixture between the transparent conductive films can cause deviations in the PDLC layer thickness. Furthermore, the mixture is prone to flow before polymerization; therefore, after being filled between a pair of transparent conductive films but before polymerization, the mixture may flow in-plane, resulting in poor thickness uniformity.

[0005] To address the aforementioned problems, the following technology has been proposed: an emulsion containing polymerized resin particles and liquid crystal particles dispersed in a solvent is coated onto a transparent conductive film with a uniform thickness, and the solvent is dried, thereby forming a PDLC layer with excellent thickness uniformity. As a specific example of this technology, a technique for coating an emulsion containing emulsified liquid crystal particles and polymer particles dispersed in water is known (Patent Document 2 or Patent Document 3).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 2550627

[0009] Patent Document 2: Japanese Patent No. 2608543

[0010] Patent Document 3: Japanese Patent No. 5355879 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] For PDLC films made using the above-mentioned emulsion, a problem may occur where liquid crystal compounds contained in the liquid crystal particles slowly leak out from the ends of the PDLC layer (liquid crystal leakage). Liquid crystal leakage not only contaminates the surrounding environment, but the properties of the PDLC film itself also change due to liquid crystal leakage.

[0013] The present invention was made to solve the above-mentioned problems, and its main objective is to provide a PDLC layer with excellent thickness uniformity and a PDLC film that suppresses liquid crystal leakage from the PDLC layer.

[0014] Problem Solving Methods

[0015] According to one aspect of the present invention, a method for manufacturing a polymer-dispersed liquid crystal film is provided, the method comprising: coating a first transparent conductive film with an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent to form a coating layer; drying the coating layer to form a polymer-dispersed liquid crystal layer comprising a polymer matrix and liquid crystal particles dispersed in the polymer matrix; and stacking a second transparent conductive film on the polymer-dispersed liquid crystal layer, wherein the polymer particles comprise first polymer particles and second polymer particles, and the average particle size of the second polymer particles is larger than the average particle size of the first polymer particles.

[0016] In one embodiment, the average particle size of the second polymer particles is 1.3 to 20 times the average particle size of the first polymer particles.

[0017] In one embodiment, the average particle size of the first polymer particles is 10 nm to 100 nm.

[0018] In one embodiment, the average particle size of the second polymer particles is 50 nm to 500 nm.

[0019] In one embodiment, the emulsion further comprises a leveling agent and / or a crosslinking agent.

[0020] According to another aspect of the present invention, a polymer-dispersed liquid crystal layer forming emulsion is provided, which is an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent, wherein the polymer particles include a first polymer particle and a second polymer particle, the average particle size of the second polymer particle being larger than the average particle size of the first polymer particle.

[0021] In one embodiment, the average particle size of the second polymer particles is 1.3 to 20 times the average particle size of the first polymer particles.

[0022] In one embodiment, the average particle size of the first polymer particles is 10 nm to 100 nm.

[0023] In one embodiment, the average particle size of the second polymer particles is 50 nm to 500 nm.

[0024] In one embodiment, the emulsion further comprises a leveling agent and / or a crosslinking agent.

[0025] According to another aspect of the present invention, a polymer-dispersed liquid crystal film is provided, which sequentially comprises a first transparent conductive film, a polymer-dispersed liquid crystal layer, and a second transparent conductive film, wherein the polymer-dispersed liquid crystal layer is formed by coating the first transparent conductive film with a polymer-dispersed liquid crystal layer forming emulsion and drying it.

[0026] In one embodiment, the thickness of the polymer-dispersed liquid crystal layer is 1 μm to 15 μm.

[0027] The effects of the invention

[0028] In this invention, a PDLC layer is prepared by coating an emulsion containing polymer particles and liquid crystal particles dispersed in a solvent and then drying it. The emulsion comprises a first polymer particle and a second polymer particle, wherein the second polymer particle has an average particle size larger than that of the first polymer particle. This results in a PDLC layer with excellent thickness uniformity and suppressed liquid crystal leakage. Attached Figure Description

[0029] Figure 1 This is a cross-sectional schematic diagram of a PDLC membrane in one embodiment of the present invention.

[0030] Symbol Explanation

[0031] 100 PDLC membrane

[0032] 10 First transparent conductive film

[0033] 20 PDLC layers

[0034] 30 Second transparent conductive film Detailed Implementation

[0035] The preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. It should be noted that in this specification, the "~" indicating a numerical range includes both the upper and lower limits of the value.

[0036] A. Manufacturing method of polymer-dispersed liquid crystal film

[0037] According to one aspect of the present invention, a method for manufacturing a PDLC film is provided, the method comprising: coating an emulsion (hereinafter sometimes referred to as "emulsion coating liquid") onto a first transparent conductive film to form a coating layer, said emulsion being an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent (step A); drying the coating layer to form a PDLC layer, said PDLC layer comprising a polymer matrix and liquid crystal particles dispersed in said polymer matrix (step B); and stacking a second transparent conductive film on said PDLC layer (step C). In the above manufacturing method, an emulsion comprising first polymer particles and second polymer particles as polymer particles is used, said second polymer particles having an average particle size larger than said first polymer particles. By coating such an emulsion coating liquid and drying it, a PDLC layer with excellent thickness uniformity and a PDLC film with suppressed liquid crystal leakage from the PDLC layer can be obtained.

[0038] The mechanism by which the above-mentioned effects are achieved can be inferred as follows, but this does not constitute any limitation on the present invention. That is, in the fabrication of a PDLC layer using an emulsion coating solution, due to solvent evaporation, the polymer particles are not completely (without gaps) fused together, but rather tiny gaps are formed between the fused particles. As a result, the liquid crystal compound is not completely encapsulated in the polymer matrix, but slowly leaks out from the ends of the PDLC layer through these gaps. Here, when the polymer particles contained in the emulsion coating solution have a small particle size, the particles are tightly aggregated and fused together, thus forming gaps with small diameters. On the other hand, gaps with few irregularities and relatively straight lines are formed (resulting in a shorter path length to the end), making liquid crystal leakage more likely. Conversely, when the polymer particles contained in the emulsion coating solution have a large particle size, the particles are fused together in a sparsely dense state, thus forming gaps with large curvatures and curves (resulting in a longer path length to the end). On the other hand, gaps with large diameters are formed, making liquid crystal leakage more likely. In contrast, by combining small polymer particles with large polymer particles, the gaps formed between polymer matrices can be made into small-diameter, curved gaps, which can suppress liquid crystal leakage.

[0039] A-1. Process A

[0040] In step A, an emulsion containing polymer particles and liquid crystal particles dispersed in a solvent is coated onto the first transparent conductive film to form a coating layer.

[0041] A-1-1. First transparent conductive film

[0042] Typically, the first transparent conductive film has a first transparent substrate and a first transparent electrode layer disposed on one side of the first transparent substrate. The first transparent conductive film may have a hard coating on one or both sides of the first transparent substrate as needed. In addition, a refractive index adjustment layer may be provided between the first transparent substrate and the first transparent electrode layer.

[0043] The surface resistivity of the first transparent conductive film is preferably 1Ω / □ to 1000Ω / □, more preferably 5Ω / □ to 300Ω / □, and even more preferably 10Ω / □ to 200Ω / □.

[0044] 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%.

[0045] The total light transmittance of the first transparent conductive film is preferably 30% or more, more preferably 60% or more, and even more preferably 80% or more.

[0046] The first transparent substrate can be formed from any suitable material. Specifically, polymeric substrates such as films and plastic substrates are preferred. This is because they offer excellent smoothness and wettability to the composition used to form the transparent electrode layer, and productivity can be significantly improved through continuous production using rollers.

[0047] Typically, the material constituting the first transparent substrate is a polymer film with thermoplastic resin as its main component. Examples of thermoplastic resins include: polyester resins; cyclic olefin resins such as polynorbornene; acrylic resins; polycarbonate resins; and cellulose resins. Among these, polyester resins, cyclic olefin resins, or acrylic resins are preferred. These resins exhibit excellent transparency, mechanical strength, thermal stability, and moisture barrier properties. The aforementioned thermoplastic resins can be used alone or in combination of two or more. Alternatively, optical films suitable for polarizers, such as low-phase-difference substrates, high-phase-difference substrates, phase-difference plates, absorptive polarizing films, and selective polarizing reflective films, can also be used as the first transparent substrate.

[0048] 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 making the thickness of the first transparent substrate 200 μm or less, the function of the PDLC layer can be fully utilized.

[0049] The total light transmittance of the first transparent substrate is preferably 30% or more, more preferably 60% or more, and even more preferably 80% or more.

[0050] The first transparent electrode layer can be formed, for example, using metal oxides such as indium tin oxide (ITO), zinc oxide (ZnO), or tin oxide (SnO2). A transparent electrode layer containing ITO is preferred. Transparent electrode layers containing ITO exhibit excellent transparency. The first transparent electrode layer can be patterned into a desired shape depending on the application.

[0051] The 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 with such a range of transmittance, high transmittance is achieved in the transparent state. The higher the transmittance, the more preferred, with an upper limit of, for example, 99%.

[0052] Preferably, the first transparent electrode layer contains grains. The presence of grains improves light transmittance. The method of grain formation is not limited; for example, grains can be suitably formed by heating in the atmosphere. The area occupancy of the 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 this area occupancy is, for example, 100%. When the area occupancy of the grains is within the above range, light transmittance is improved. It should be noted that the area occupancy of the grains can be calculated by observing the surface of the transparent electrode layer using a transmission electron microscope (TEM) and based on the area ratio of the crystalline region to the amorphous region.

[0053] 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, there is a risk of poor adhesion to the substrate. The upper limit of the surface roughness Ra of the first transparent electrode layer is preferably less than 1.2 nm, more preferably less than 1.0 nm, further preferably less than 1.0 nm, and particularly preferably less than 0.8 nm. When the surface roughness Ra of the first transparent electrode layer is too large, there is a risk of difficulty in properly forming grains. It should be noted that the surface roughness Ra in this specification refers to the arithmetic mean roughness Ra measured by AFM (Atomic Force Microscope).

[0054] 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, there is a risk of reduced grain area occupancy. 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 even more preferably 27 nm or less. When the thickness of the transparent electrode layer exceeds 50 nm, there is a risk of decreased transmittance, and also a risk of increased surface roughness of the transparent electrode layer.

[0055] The first transparent electrode layer can be formed on one side of the first transparent substrate, for example, by sputtering. After the metal oxide layer is formed by sputtering, crystallization can occur by annealing. Annealing can be performed, for example, by heat treatment at 120°C to 300°C for 10 to 120 minutes.

[0056] The refractive index adjustment layer can control the hue and / or transmittance of the PDLC film. The refractive index adjustment layer can consist of a single layer or a stack of two or more layers.

[0057] The refractive index of the refractive index adjustment layer is preferably 1.3 to 1.8, more preferably 1.35 to 1.7, and even more preferably 1.38 to 1.68. In the case of a single layer, for example, when the transparent electrode layer is ITO, it is more desirable to have a low refractive index, for example, preferably 1.38 to 1.46, rather than to optically mitigate the refractive index of ITO. This allows for a suitable reduction of interfacial reflection between the transparent substrate and the transparent electrode layer.

[0058] The refractive index adjustment layer can be formed from inorganic materials, organic materials, or mixtures of inorganic and organic materials. Examples of materials that can form the refractive index adjustment layer include: NaF, Na3AlF6, LiF, MgF2, CaF2, SiO2, LaF3, CeF3, Al2O3, TiO2, Ta2O5, ZrO2, ZnO, ZnS, and SiO2. x Inorganic materials such as (x is 1.5 or more and less than 2), acrylic resins, epoxy resins, urethane resins, melamine resins, alkyd resins, and siloxane polymers, etc., are also used. In particular, thermosetting resins containing a mixture of melamine resin, alkyd resin and organosilane condensates are preferred as organic materials.

[0059] The refractive index adjustment layer can also contain nanoparticles with an average particle size of 1 nm to 100 nm. By including nanoparticles in the refractive index adjustment layer, the refractive index of the refractive index adjustment layer itself can be easily adjusted.

[0060] The content of nanoparticles in the refractive index adjustment layer is preferably 0.1 wt% to 90 wt%. Furthermore, the content of nanoparticles in the refractive index adjustment layer is more preferably 10 wt% to 80 wt%, and even more preferably 20 wt% to 70 wt%.

[0061] Examples of inorganic oxides that can form nanoparticles include: silicon dioxide, hollow nano-silica, titanium dioxide, aluminum oxide, zinc oxide, tin oxide, zirconium oxide, and niobium oxide. Among these, silicon dioxide, titanium dioxide, aluminum oxide, zinc oxide, tin oxide, zirconium oxide, and niobium oxide are preferred. These inorganic oxides can be used alone or in combination of two or more.

[0062] The thickness of the refractive index adjustment layer is preferably 10 nm to 200 nm, more preferably 20 nm to 150 nm, and even more preferably 30 nm to 130 nm. If the thickness of the refractive index adjustment layer is too small, it is not easy to form a continuous film. In addition, if the thickness of the refractive index adjustment layer is too large, there is a tendency for the transparency to decrease in the transparent state or for cracks to easily form.

[0063] The refractive index adjustment layer can be formed by using the above-mentioned materials and by coating methods such as wet coating, gravure coating, bar coating, vacuum evaporation, sputtering, and ion plating.

[0064] A-1-2. Emulsion Topical Solution

[0065] The emulsion coating liquid comprises a solvent, and polymer particles and liquid crystal particles dispersed in the solvent. The polymer particles comprise a first polymer particle and a second polymer particle, wherein the second polymer particle has an average particle size greater than the average particle size of the first polymer particle. The emulsion coating liquid preferably further comprises a leveling agent and / or a crosslinking agent.

[0066] The average particle size of the first polymer particles is preferably 10 nm to 100 nm, more preferably 15 nm to 90 nm, and even more preferably 20 nm to 80 nm. If the average particle size of the first polymer particles is less than 10 nm, due to the high surface free energy, only the first polymer particles will aggregate during the drying of the coating layer, which may sometimes lead to insufficient suppression of liquid crystal leakage. Furthermore, if the average particle size of the first polymer particles exceeds 100 nm, the difference between the average particle size of the first polymer particles and the second polymer particles becomes smaller, which may sometimes lead to insufficient suppression of liquid crystal leakage. It should be noted that the average particle size of the first and second polymer particles refers to the volume-average median particle size, which can be measured using a dynamic light scattering particle size distribution measuring device.

[0067] The coefficient of variation (CV value) of the average particle size of the first polymer particles can be less than 1.0, preferably less than 0.5, and more preferably 0.2 to 0.4.

[0068] The polymer forming the first polymer particles can be appropriately selected based on factors such as light transmittance, the refractive index of the liquid crystal particles and the second polymer particles, and the adhesion to the transparent conductive film. The polymer forming the first polymer particles can be an optically isotropic resin or an optically anisotropic resin. Examples of such polymers include water-dispersible resins, such as polyurethane, polyether, polyester, polycarbonate, or acrylic water-dispersible resins. Water-dispersible resins of polyurethane or acrylic types are preferred.

[0069] The average particle size of the second polymer particles is preferably 50 nm to 500 nm, more preferably 80 nm to 400 nm, and even more preferably 100 nm to 300 nm. When the average particle size of the second polymer particles is less than 50 nm, the difference between the average particle size of the second polymer particles and the first polymer particles becomes smaller, which may sometimes lead to insufficient suppression of liquid crystal leakage. In addition, when the average particle size of the second polymer particles exceeds 500 nm, it may sometimes be impossible to mix uniformly with the first polymer particles, resulting in interpolymer light diffusion. As a result, it may sometimes be impossible to obtain a PDLC film with high transparency in a transparent state.

[0070] The coefficient of variation (CV value) of the average particle size of the second polymer particles can be less than 1.0, preferably less than 0.5, and more preferably 0.2 to 0.4.

[0071] The polymer forming the second polymer particles can be appropriately selected based on factors such as light transmittance, the refractive index of the liquid crystal particles and the first polymer particles, and the adhesion to the transparent conductive film. The polymer forming the second polymer particles can be an optically isotropic resin or an optically anisotropic resin. Examples of this polymer include the same polymer used to form the first polymer particles. The first polymer particles and the second polymer particles can be formed from the same type of polymer or from different types of polymers.

[0072] The ratio of the average particle size of the second polymer particles to the average particle size of the first polymer particles (average particle size of the second polymer particles / average particle size of the first polymer particles) is preferably 1.3 to 20, more preferably 1.3 to 10, and even more preferably 1.5 to 5. When this ratio is less than 1.3, the suppression effect on liquid crystal leakage may sometimes become insufficient. In addition, when this ratio exceeds 20, the first polymer particles and the second polymer particles may sometimes fail to mix uniformly.

[0073] The proportion of polymer particles in the solid component of the emulsion coating (the total proportion of the first polymer particle and the second polymer particle) is preferably 70% by weight or less, more preferably 40% to 60% by weight.

[0074] The ratio of the first polymer particles to the second polymer particles in the emulsion coating solution (the former: the latter, by weight) is preferably 2:8 to 8:2, more preferably 3:7 to 7:3.

[0075] As the liquid crystal compound for forming the above-mentioned liquid crystal particles, any suitable liquid crystal compound can be used, but it is preferred to use one with a birefringence Δn (=n) of 0.05 to 0.25 at a wavelength of 589 nm. e -n o ;n e n is the refractive index along the long axis of the liquid crystal compound molecule. o (Refractive index of the liquid crystal compound molecules along the short axis), more preferably, a liquid crystal compound having a birefringence Δn of 0.05 to 0.20 is used.

[0076] The dielectric anisotropy of a liquid crystal compound can be either positive or negative. Liquid crystal compounds can be, for example, nematic, smectic, or cholesteric liquid crystal compounds. Since excellent transparency can be achieved in the transparent state, nematic liquid crystal compounds are preferred. Examples of such nematic liquid crystal compounds include: biphenyl compounds, phenyl benzoate compounds, cyclohexylbenzene compounds, azobenzene compounds, azomethyl base compounds, terphenyl compounds, biphenyl benzoate compounds, cyclohexylbiphenyl compounds, phenylpyridine compounds, cyclohexylpyrimidine compounds, cholesterol compounds, and fluorine compounds.

[0077] The average particle size of the liquid crystal particles is preferably 1 μm or more, more preferably 2 μm or more. Furthermore, the average particle size of the liquid crystal particles is preferably 9 μm or less, more preferably 8 μm or less. When the average particle size of the liquid crystal particles is within this range, the average particle size of the liquid crystal droplets in the PDLC layer can reach the desired range. It should be noted that the above-mentioned average particle size of the liquid crystal particles is the volume average particle size.

[0078] The average particle size of the liquid crystal particles preferably has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the average particle size of the liquid crystal particles can be less than 0.40, preferably less than 0.35, and more preferably less than 0.30. In one embodiment, an emulsion coating liquid that substantially does not contain liquid crystal capsules with a particle size of less than 1 μm or more than 9 μm can be used (e.g., an emulsion coating liquid in which the volume of liquid crystal particles with a particle size of less than 1 μm or more than 9 μm is 10% or less relative to the total volume of liquid crystal particles).

[0079] The proportion of liquid crystal particles in the solid component of the emulsion coating liquid is preferably 30% by weight or more, more preferably 40% to 60% by weight.

[0080] As described above, the emulsion coating solution preferably further includes a leveling agent. The liquid crystal particles in the emulsion coating solution have a particle size in the micrometer range, while the polymer particles have a particle size in the nanometer range. Therefore, after the solvent evaporates from the coating layer through drying, the thickness of the areas where liquid crystal particles are dispersed increases locally compared to the undispersed areas. As a result, fine unevenness is generated on the surface of the dried coating film with a period of several μm to tens of μm. Such unevenness can lead to the entrapment of tiny air bubbles during the lamination of the second transparent conductive film, which may reduce transparency and reliability when voltage is applied. Therefore, by adding a leveling agent, such unevenness can be suppressed, preventing the entrapment of tiny air bubbles during the lamination of the second transparent conductive film.

[0081] Examples of leveling agents include acrylic leveling agents, fluorinated leveling agents, and silicone leveling agents. Examples of acrylic leveling agents include Polyflow No. 36, Polyflow No. 56, Polyflow No. 85HF, and Polyflow No. 99C (all manufactured by Kyoeisha Chemical Co., Ltd.). Examples of fluorinated leveling agents include MEGAFAC F444, MEGAFACF470N, and MEGAFAC F556 (all manufactured by DIC Corporation). Examples of silicone leveling agents include LE303 (manufactured by Kyoeisha Chemical Co., Ltd.) and Grandic PC4100 (manufactured by DIC Corporation).

[0082] The leveling agent is preferably contained in 0.05 to 10 parts by weight, more preferably 0.1 to 1 part by weight, relative to 100 parts by weight of the emulsion coating liquid.

[0083] In addition, the emulsion coating liquid may also contain a crosslinking agent. By using a crosslinking agent, a PDLC layer comprising a polymer matrix having a crosslinked structure can be formed.

[0084] As a crosslinking agent, any suitable crosslinking agent can be used. Examples include aziridine crosslinking agents and isocyanate crosslinking agents.

[0085] The crosslinking agent is preferably contained in 0.5 to 10 parts by weight, more preferably 0.8 to 5 parts by weight, relative to 100 parts by weight of the emulsion coating.

[0086] Emulsion coating solutions can be prepared, for example, by mixing a resin emulsion containing first polymer particles, a resin emulsion containing second polymer particles, a liquid crystal emulsion containing liquid crystal particles, and any component (e.g., a leveling agent, a crosslinking agent). Solvents and dispersants may be further added during mixing as needed. Alternatively, emulsion coating solutions can be prepared by adding a liquid crystal compound and a water-dispersible resin to a solvent and dispersing them mechanically. It should be noted that water, or a mixture of water and a water-miscible organic solvent, is preferably used as the solvent.

[0087] The aforementioned resin emulsions and liquid crystal emulsions can be prepared, for example, by mechanical emulsification, microchannel method, membrane emulsification, etc. Liquid crystal emulsions are preferably prepared by membrane emulsification. According to membrane emulsification, emulsions with uniform particle size distribution can be readily obtained. For details regarding membrane emulsification, please refer to the disclosures in Japanese Patent Application Publication No. 4-355719 and Japanese Patent Application Publication No. 2015-40994 (which are incorporated herein by reference).

[0088] The concentration of solid components in the emulsion application solution can be, for example, 20% to 60% by weight, preferably 30% to 50% by weight.

[0089] The viscosity of the emulsion coating solution can be appropriately adjusted to allow for suitable coating of the first transparent conductive film. The viscosity of the emulsion coating solution 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, solvent convection becomes significant during drying, potentially leading to instability in the thickness of the PDLC layer. Furthermore, when the viscosity exceeds 400 mPas, there is a risk of instability in the emulsion coating solution. The viscosity of the emulsion coating solution can be measured, for example, using a rheometer MCR302 manufactured by Anton Paar. The viscosity used here is the shear viscosity value under conditions of 20°C and a shear rate of 1000 (1 / s).

[0090] A-1-3. Coating

[0091] Typically, the above-mentioned PDLC forming emulsion can be coated on the transparent electrode layer side surface of the first transparent conductive film.

[0092] As a coating method for the emulsion used in PDLC formation, any suitable method can be used. Examples include: roller coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, and blade coating (such as comma coating). Among these, roller coating is preferred. For example, regarding coating based on roller coating using a slit die, please refer to the description in Japanese Patent Application Publication No. 2019-5698.

[0093] The thickness of the coating layer is preferably 3 μm to 40 μm, more preferably 4 μm to 30 μm, and even more preferably 5 μm to 20 μm. If it is within this range, a PDLC layer with excellent thickness uniformity can be obtained.

[0094] A-2. Process B

[0095] In step B, the coating layer is dried to form a PDLC layer. In one embodiment, the PDLC layer becomes transparent when a voltage is applied and becomes scattering when no voltage is applied (normal mode). In another embodiment, the PDLC layer becomes scattering when a voltage is applied and becomes transparent when no voltage is applied (reverse mode).

[0096] The coating layer can be dried by any suitable method. Specific examples of drying methods include heat drying and hot air drying. When the emulsion coating liquid contains a crosslinking agent, a crosslinked structure of the polymer matrix can be formed during drying.

[0097] 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. By appropriately setting the drying temperature and drying time, a PDLC layer with the first and second polymer particles fused together and excellent liquid crystal leakage can be obtained.

[0098] The PDLC layer comprises a polymer matrix and liquid crystal particles dispersed in the polymer matrix. The polymer forming the polymer matrix and the liquid crystal compound contained in the liquid crystal particles are described in section A-1.

[0099] The polymer matrix content in the PDLC layer is preferably 80% by weight or less, more preferably 70% by weight or less, even more preferably 60% by weight or less, and preferably 35% by weight or more, more preferably 40% by weight or more. In one embodiment, this content is 35% to 70% by weight. When the polymer matrix content is less than 35% by weight, the liquid crystal particles are independent of each other in the polymer and do not disperse, at least locally forming a continuous phase, which may lead to liquid crystal leakage. In addition, problems such as damage to the mechanical strength of the PDLC layer may also occur. On the other hand, when the polymer matrix content exceeds 80% by weight, problems such as increased driving voltage and reduced dimming function may occur.

[0100] The liquid crystal compound in the PDLC layer preferably contains 20% by weight or more, more preferably 30% by weight or more, and even more preferably 40% by weight or more. It is also preferably 65% ​​by weight or less, more preferably 60% by weight or less. In one embodiment, this content is 20% to 65% by weight.

[0101] The average particle size of the liquid crystal particles (liquid crystal droplets) in the PDLC layer can be, for example, 1 μm to 9 μm, preferably 2 μm to 8 μm. If the average particle size is too small, the proportion of long-wavelength light in the transmitted light in the transparent state increases, potentially resulting in an orange hue. Conversely, if the average particle size is too large, the proportion of short-wavelength light in the transmitted light in the transparent state increases, potentially resulting in a blue hue. It should be noted that the average particle size of the liquid crystal particles in the PDLC layer described above is the volume average particle size of the liquid crystal particles when viewed from a direction perpendicular to the main surface of the PDLC film.

[0102] The thickness of the PDLC layer is, for example, 1 μm to 15 μm, preferably 1 μm to 12 μm, and more preferably 2 μm to 10 μm. By making the thickness of the PDLC layer 15 μm or less, the area of ​​the PDLC layer exposed at the end can be reduced, which helps to prevent liquid crystal leakage from the end.

[0103] A-3. Process C

[0104] In step C, a second transparent conductive film is laminated on the PDLC layer. Thus, a PDLC film having a first transparent conductive film, a PDLC layer, and a second transparent conductive film in sequence can be obtained.

[0105] Typically, the second conductive film has a second transparent substrate and a second transparent electrode layer disposed on one side of the second transparent substrate. The second transparent conductive film may also have a hard coating on one or both sides of the second transparent substrate as needed. Additionally, a refractive index adjustment layer may be provided between the second transparent substrate and the second transparent electrode layer.

[0106] The surface resistivity of the second transparent conductive film is preferably 1Ω / □ to 1000Ω / □, more preferably 5Ω / □ to 300Ω / □, and even more preferably 10Ω / □ to 200Ω / □.

[0107] 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%.

[0108] The total light transmittance of the second transparent conductive film is preferably 30% or more, more preferably 60% or more, and even more preferably 80% or more.

[0109] The same descriptions as those for the first transparent substrate and the first transparent electrode layer apply to the second 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 it may have a different structure.

[0110] The second transparent conductive film is laminated on the PDLC layer such that the second transparent electrode layer side is opposite to the PDLC layer. From the viewpoint of obtaining sufficient adhesion, this lamination is preferably performed simultaneously using a laminator with a lamination pressure of 0.006 MPa / m to 7 MPa / m, more preferably 0.06 MPa / m to 0.7 MPa / m.

[0111] B. Polymer-dispersed liquid crystal film

[0112] The polymer-dispersed liquid crystal film of the present invention comprises, in sequence, a first transparent conductive film, a PDLC layer, and a second transparent conductive film.

[0113] Figure 1 This is a cross-sectional schematic diagram of a PDLC film according to one embodiment of the present invention. The PDLC film 100 sequentially includes a first transparent conductive film 10, a PDLC layer 20, and a second transparent conductive film 30. The first transparent conductive film 10 has a first transparent substrate 12 and a first transparent electrode layer 14 disposed on one side (PDLC layer 20 side). In addition, the second transparent conductive film 30 has a second transparent substrate 32 and a second transparent electrode layer 34 disposed on one side (PDLC layer 20 side).

[0114] Regarding the first transparent conductive film 10, the PDLC layer 20, and the second transparent conductive film 30, as described in section A.

[0115] The PDLC layer is formed by coating the emulsion coating liquid described in item A-1-2 onto the first transparent conductive film and drying it. Since the emulsion coating liquid contains the first polymer particles and the second polymer particles having an average particle size larger than the average particle size of the first polymer particles, it can have a polymer matrix structure that is not prone to liquid crystal leakage.

[0116] The overall thickness of the PDLC film is, for example, 30 μm to 250 μm, preferably 50 μm to 150 μm.

[0117] Example

[0118] The present invention will now be described in detail with reference to embodiments, but the present invention is not limited to these embodiments in any way. The methods for measuring each characteristic are described below. Furthermore, unless otherwise explicitly stated, "parts" and "%" in the embodiments and comparative examples are based on weight.

[0119] (1) Thickness

[0120] The measurements were performed using a digital micrometer (manufactured by Anritsu, product name "KC-351C").

[0121] (2) Average particle size of polymer particles

[0122] A few drops of resin dispersion were added to 100 mL of water to prepare the test sample. Using a dynamic light scattering particle size distribution analyzer (Microtrac, device name "Nanotrac 150"), the test sample was placed on the analyzer's frame, and the concentration was measured after confirming the measurable concentration using the analyzer's monitor.

[0123] (3) Volume average particle size of liquid crystal particles in PDLC layer

[0124] After peeling off the second transparent conductive film of the PDLC film to expose the PDLC layer, the surface of the exposed PDLC layer was measured with a transmission optical microscope at 100x objective lens in a 100μm square field of view. The focus was gradually changed while measuring the particle size of each liquid crystal particle at the most aligned focal position in 0.1μm units. Statistical processing was performed based on volume to calculate the volume average particle size and the calculated volume variation coefficient (CV value).

[0125] CV value = Standard deviation of particle distribution on a volume basis / Volume average particle size

[0126] (4) Volume average particle size of liquid crystal capsules in liquid crystal emulsion

[0127] 0.1% by weight of liquid crystal emulsion was added to 200 ml of an electrolyte aqueous solution (Coulter, "ISOTON II"). The resulting mixture was used as the test sample. Using a Multisizer 3 (Coulter, pore size = 20 μm), 256 portions were divided at logarithmic intervals from 0.4 μm to 12 μm. The volume of each discretized particle size was statistically analyzed, and the volume average particle size and the calculated volume variation coefficient (CV) were calculated. It should be noted that in the presence of particles larger than 12 μm, the pore size was set to 30 μm, and 256 portions were divided at logarithmic intervals from 0.6 μm to 18 μm. The volume of each discretized particle size was statistically analyzed, and the volume average particle size and CV value were calculated accordingly.

[0128] CV value = Standard deviation of particle distribution on a volume basis / Volume average particle size

[0129] [Example 1]

[0130] (First and second transparent conductive films)

[0131] An ITO layer was formed on one side of a PET substrate (thickness: 50 μm) by sputtering, resulting in a transparent conductive film with a structure of [transparent substrate / transparent electrode layer].

[0132] (Preparation of lotion application solution)

[0133] A liquid crystal emulsion was prepared by mixing 59.7 parts of a mixed liquid crystal compound (manufactured by JNC Corporation, product name "LX-153XX", birefringence Δn = 0.149 (ne = 1.651, no = 1.502), viscosity = 48.5 mPa·s), 39.8 parts of pure water, and 0.5 parts of a dispersant (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., "Noigen ET159"), stirring at 100 rpm for 10 minutes using a homogenizer. The average particle size of the liquid crystal particles in the obtained liquid crystal emulsion was 3.4 μm.

[0134] By mixing 38.4 parts of the above liquid crystal emulsion, 19.1 parts of an aqueous dispersion of polyether polyurethane resin (manufactured by DSM Corporation, trade name "NeoRez R967", average polymer particle size: 80 nm, CV value = 0.27, solid content: 40 wt%), 17.0 parts of an aqueous dispersion of polyester polyurethane resin (manufactured by Sanyo Chemical Co., Ltd., trade name "UCOAT C-102", average polymer particle size: 168 nm, CV value = 0.23, solid content: 45 wt%), 0.1 parts of a leveling agent (manufactured by DIC Corporation, product name "F-444"), 1.1 parts of a crosslinking agent (propylidynetrimethyltris[3-(2-methylaziridin-1-yl)propionate]), and 24.3 parts of pure water, an emulsion coating solution (solid content concentration: 40 wt%) was obtained.

[0135] (Application and drying of emulsion)

[0136] The aforementioned emulsion coating solution was applied to the ITO layer of the first transparent conductive film to form a coating layer with a thickness of 20 μm. Coating was performed using a slit die at a linear speed of 6 m / min. The coating layer was then dried at 25°C for 8 minutes to form a PDLC layer with a thickness of 8 μm.

[0137] (Layering of the second transparent conductive film)

[0138] A second transparent conductive film was laminated onto the PDLC layer using a laminator and a lamination pressure of 0.4 MPa / m, with the ITO layer facing the PDLC layer. This yielded the PDLC film.

[0139] [Example 2]

[0140] An emulsion coating solution was prepared by setting the amount of the polyether-based polyurethane resin aqueous dispersion to 12.8 parts and the amount of the polyester-based polyurethane resin aqueous dispersion to 22.8 parts. Otherwise, a PDLC membrane was obtained in the same manner as in Example 1.

[0141] [Example 3]

[0142] An emulsion coating was prepared by replacing the liquid crystal compound (product name "LX-153XX") with a liquid crystal compound (manufactured by JNC Corporation, product name "LX-154XX", birefringence Δn = 0.198 (ne = 1.709, no = 1.511), viscosity: 57.5 mPa·s). Otherwise, a PDLC film was obtained in the same manner as in Example 1.

[0143] [Example 4]

[0144] An isocyanate-cured hydroxyl-containing acrylic resin emulsion (manufactured by DIC, product name "Burnock WE-314", average polymer particle size: 140 nm, CV value = 0.25, solid content: 45 wt%) was used instead of a polyester-based polyurethane resin aqueous dispersion. The amount of liquid crystal emulsion was set to 32.4 parts, the amount of polyether-based polyurethane resin aqueous dispersion was set to 11.5 parts, the amount of isocyanate-cured hydroxyl-containing acrylic resin emulsion was set to 30.8 parts, the amount of leveling agent was set to 0.04 parts, the amount of crosslinking agent was set to 1.4 parts, and the amount of pure water was set to 13.6 parts. An emulsion coating solution was prepared, and a PDLC film was obtained in the same manner as in Example 1.

[0145] [Comparative Example 1]

[0146] An emulsion coating solution was prepared by setting the amount of the polyether-based polyurethane resin aqueous dispersion to 0 parts and the amount of the polyester-based polyurethane resin aqueous dispersion to 34.7 parts. Otherwise, a PDLC membrane was obtained in the same manner as in Example 1.

[0147] The optical properties and liquid crystal leakage of the PDLC films obtained in the Examples and Comparative Examples were evaluated using the methods described below. The results are shown in Table 1 together with the composition of the emulsion coating solution.

[0148] Optical Properties

[0149] Using an AC power supply “EC750SA” manufactured by NF Circuit Design Co., Ltd., the haze was measured when an AC voltage of 30V was applied to the PDLC film obtained in the above examples and comparative examples and when no AC voltage was applied.

[0150] Evaluation Methods for Liquid Crystal Leakage

[0151] Multiple PDLC films cut to A4 size are stacked together. The resulting block is sandwiched between a 2mm thick transparent polycarbonate plate, or a 1kg weight is placed on it. The plate is left at room temperature for 24 hours, continuously applying surface pressure to the PDLC films. Then, observations are made between the PDLC films or between the PDLC films and the polycarbonate plate. If at least one seepage mark of 1mm × 1mm or larger is confirmed, liquid crystal leakage is considered "present"; if no such seepage mark is confirmed, liquid crystal leakage is considered "absent". It should be noted that the seepage is caused by liquid (liquid crystal compound) leaking from the ends of the PDLC films and permeating between the PDLC films or between the PDLC films and the polycarbonate plate.

[0152] [Table 1]

[0153]

[0154] As shown in Table 1, liquid crystal leakage occurred in the PDLC film of the comparative example, while liquid crystal leakage was prevented in the PDLC film of the embodiment. Furthermore, since the PDLC film of the embodiment was formed using an emulsion coating solution, the uniformity of the PDLC layer thickness was excellent.

[0155] Industrial applicability

[0156] The PDLC film of the present invention can be used for various applications such as blinds or curtains, displays, and projection screens.

Claims

1. A method for manufacturing a polymer-dispersed liquid crystal film, the method comprising: An emulsion is coated onto a first transparent conductive film to form a coating layer, wherein the emulsion is an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent; The coating layer is dried to form a polymer-dispersed liquid crystal layer, the polymer-dispersed liquid crystal layer comprising a polymer matrix and liquid crystal particles dispersed in the polymer matrix; and A second transparent conductive film is stacked on the polymer-dispersed liquid crystal layer. in, The polymer particle comprises a first polymer particle and a second polymer particle. The average particle size of the second polymer particle is larger than the average particle size of the first polymer particle. The average particle size of the second polymer particle is 1.3 to 20 times that of the average particle size of the first polymer particle.

2. The manufacturing method according to claim 1, wherein, The average particle size of the first polymer particles is 10 nm to 100 nm.

3. The manufacturing method according to claim 1, wherein, The average particle size of the second polymer particles is 50 nm to 500 nm.

4. The manufacturing method according to claim 1, wherein, The emulsion further comprises a leveling agent and / or a crosslinking agent.

5. A polymer-dispersed liquid crystal layer forming emulsion, which is an emulsion in which polymer particles and liquid crystal particles are dispersed in a solvent, wherein, The polymer particle comprises a first polymer particle and a second polymer particle. The average particle size of the second polymer particle is larger than the average particle size of the first polymer particle. The average particle size of the second polymer particle is 1.3 to 20 times that of the average particle size of the first polymer particle.

6. The emulsion according to claim 5, wherein, The average particle size of the first polymer particles is 10 nm to 100 nm.

7. The emulsion according to claim 5, wherein, The average particle size of the second polymer particles is 50 nm to 500 nm.

8. The emulsion according to claim 5, further comprising a leveling agent and / or a crosslinking agent.

9. A polymer-dispersed liquid crystal film, comprising, in sequence, a first transparent conductive film, a polymer-dispersed liquid crystal layer, and a second transparent conductive film. The polymer-dispersed liquid crystal layer is formed by coating the first transparent conductive film with the polymer-dispersed liquid crystal layer forming emulsion as described in any one of claims 5 to 8 and then drying it.

10. The polymer-dispersed liquid crystal film according to claim 9, wherein, The thickness of the polymer-dispersed liquid crystal layer is 1μm to 15μm.

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