Polymer dispersed liquid crystal film and use method thereof

Abstract

This invention provides a polymer-dispersed liquid crystal film with a design that can be modified for temporary application. The polymer-dispersed liquid crystal film of this invention has a polymer-dispersed liquid crystal layer comprising a polymer matrix and droplets, wherein the droplets are dispersed in the polymer matrix and contain a liquid crystal compound, and the liquid crystal compound comprises a photoreactive liquid crystal compound having at least two reversible photodimeric functional groups.

Description

Technical Field

[0001] The present invention relates to a polymer dispersed liquid crystal film and a method for using the polymer dispersed liquid crystal film. Prior Art

[0002] A polymer-dispersed liquid crystal (PDLC) film, sometimes referred to as "PDLC," has a layer composed of a polymer matrix and liquid crystal compound droplets between a pair of transparent electrode layers. The PDLC film can change the degree of light scattering through the PDLC layer depending on the applied voltage. For example, by switching between an applied voltage and an unapplied voltage, the PDLC film can switch between a light-scattering state (scattering state) and a light-transmitting state (transparent state) (Patent Document 1). Research is underway to utilize this capability in applications such as advertising, signage, and smart windows. Prior Art Literature Patent Literature

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-189123 Summary of the Invention

[0004] [Problems to be solved by the invention]

[0005] The present inventors have discovered that by using a polymerizable liquid crystal compound to form a PDLC film and polymerizing the polymerizable liquid crystal compound in desired regions, the PDLC film can be given a desired design. This method can produce a PDLC film with a desired design, but the temporarily applied design is irreversible and cannot be changed to another design.

[0006] The main object of the present invention is to provide a PDLC film that can change the temporarily applied design. [Technical means to solve the problem]

[0007] [1] According to one aspect of the present invention, a polymer dispersed liquid crystal film is provided, which has a polymer dispersed liquid crystal layer comprising a polymer matrix and droplets, wherein the droplets are dispersed in the polymer matrix and contain a liquid crystal compound, and the liquid crystal compound contains a photoreactive liquid crystal compound having at least two reversible photodimerization functional groups. [2] In the polymer dispersed liquid crystal film described in [1] above, the liquid crystal compound may further include a non-reactive liquid crystal compound. [3] In the polymer dispersed liquid crystal film as described in [1] or [2] above, the reversible photodimerization functional group can be selected from anthracene, coumarin, cinnamic acid, stilbene and thymine groups. [4] In the polymer dispersed liquid crystal film described in any one of [1] to [3] above, the photoreactive liquid crystal compound may include a photoreactive liquid crystal compound having three or more of the above-mentioned reversible photodimerization functional groups. [5] In the polymer dispersed liquid crystal film described in any one of [1] to [4] above, there may be a substrate with a transparent electrode layer arranged on both sides of the polymer dispersed liquid crystal layer. [6] In the polymer dispersed liquid crystal film described in any one of [1] to [5] above, the amount of change in haze between a voltage applied state and a voltage not applied state can be changed by the reversible photodimerization reaction of the photoreactive liquid crystal compound. [7] According to another aspect of the present invention, a method for using a polymer-dispersed liquid crystal film is provided, which is the method for using a polymer-dispersed liquid crystal film as described in any one of [1] to [6] above, and includes: a fixing step, in which a liquid crystal polymer is generated by a photodimerization reaction of the photoreactive liquid crystal compound; and a resetting step, in which a depolymerization reaction of the liquid crystal polymer is generated to generate the photoreactive liquid crystal compound. [8] In the method for using the polymer dispersed liquid crystal film as described in [7] above, the above fixing step can be performed again after the above resetting step. [9] In the method for using the polymer dispersed liquid crystal film as described in [7] or [8] above, the above fixing step and the above resetting step can be repeated.

[10] In the method for using a polymer dispersed liquid crystal film as described in [8] or [9] above, the region where the liquid crystal polymer is generated in the second or subsequent fixing steps may be different from the region where the liquid crystal polymer is generated in the previous fixing step. [Effects of the Invention]

[0008] According to an embodiment of the present invention, a PDLC film is provided. The PDLC film can change a temporarily applied design by using a photoreactive liquid crystal compound having a reversible photodimerization functional group as a liquid crystal compound. Simple diagram description

[0009] 1( a ) and ( b ) are schematic cross-sectional views illustrating the structure of a PDLC film according to one embodiment of the present invention. FIG2 is a schematic cross-sectional view illustrating the structure of a PDLC film in another embodiment of the present invention. 3( a ) to ( e ) are schematic diagrams illustrating a method for using a PDLC film according to an embodiment of the present invention. 4( a ) to ( e ) are schematic diagrams illustrating a method for using a PDLC film according to another embodiment of the present invention. FIG. 5 is a schematic diagram illustrating a method for using a PDLC film according to another embodiment of the present invention. FIG6 is a graph showing changes in haze when voltage is applied to the PDLC film of the example. FIG. 7 is a graph showing the haze of the PDLC film of the embodiment in a state where no voltage is applied in each step. Implementation Method

[0010] The following describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments. In addition, in this specification, "~" indicating a numerical range includes its upper limit and lower limit.

[0011] A. Polymer dispersed liquid crystal film According to one aspect of the present invention, a PDLC film is provided, comprising a PDLC layer comprising a polymer matrix and liquid droplets. The liquid droplets are dispersed in the polymer matrix and contain a liquid crystal compound, wherein the liquid crystal compound comprises a photoreactive liquid crystal compound having at least two reversible photodimerization functional groups. The photoreactive liquid crystal compound can be gradually polymerized via a photodimerization reaction to form a liquid crystal polymer. Furthermore, the resulting liquid crystal polymer can be decomposed via a depolymerization reaction to form the photoreactive liquid crystal compound (in other words, return to the photoreactive liquid crystal compound). Because these reactions are reversible, the PDLC film of this embodiment of the present invention can utilize the polymerization and depolymerization of the photoreactive liquid crystal compound to arbitrarily form regions with varying haze or varying haze levels, thereby applying a desired design. Furthermore, a temporarily applied design can be modified. Therefore, the PDLC film of this embodiment of the present invention can be used, for example, as a rewritable dimming film or a diffuser film.

[0012] A-1. Overall structure of PDLC film Figure 1 is a schematic cross-sectional view illustrating the structure of a PDLC film according to one embodiment of the present invention. PDLC film 100A comprises a PDLC layer 10 containing a polymer matrix 12 and droplets of a liquid crystal compound (hereinafter sometimes referred to as "liquid crystal droplets") 14 dispersed within the polymer matrix 12. The liquid crystal droplets 14 contain, as liquid crystal compounds, a photoreactive liquid crystal compound 15 having at least two reversibly photodimerizable functional groups and a non-reactive liquid crystal compound 16. The PDLC film 100A comprises a first substrate 20 on one side of the PDLC layer 10 and a second substrate 30 on the other side. The first substrate 20 and the second substrate 30 comprise substrate bodies 22 and 32 and transparent electrode layers 24 and 34, respectively.

[0013] The PDLC film 100A shown in Figure 1 is in a normal mode. Specifically, as shown in Figure 1(a), when no voltage is applied, the photoreactive liquid crystal compounds 15 and non-reactive liquid crystal compounds 16 in the liquid crystal droplets 14 are not aligned. Due to the refractive index difference between the polymer matrix 12 and the liquid crystal droplets 14, scattering occurs, resulting in a scattering state. On the other hand, as shown in Figure 1(b), when a voltage is applied, the photoreactive liquid crystal compounds 15 and non-reactive liquid crystal compounds 16 align along the direction of the electric field, aligning the refractive index of the liquid crystal droplets 14 with that of the polymer matrix 12. This results in a transparent state with lower haze than the scattering state. The PDLC film according to an embodiment of the present invention can also differ from the illustrated example and be in a reverse mode, in which the film is in a scattering state when voltage is applied and in a transparent state with lower haze than the scattering state when no voltage is applied.

[0014] The PDLC film 100A typically utilizes the reversible photodimerization reaction of the photoreactive liquid crystal compound 15 to change the amount of haze change between the voltage-applied and non-voltage-applied states, as described in detail in Section B. Specifically, by utilizing photodimerization to gradually polymerize the photoreactive liquid crystal compound, the amount of haze change between the voltage-applied and non-voltage-applied states can be reduced. This haze change can be restored by depolymerizing the photoreactive liquid crystal compound.

[0015] The voltage applied to the PDLC film 100A in the voltage-applied state is a voltage capable of operating the PDLC film 100A (operating voltage), and may be, for example, 5 V to 200 V, preferably 10 V to 100 V. In this specification, the "voltage-applied state" refers to a state in which an operating voltage is applied to the PDLC film, such as a state in which a voltage of 50 V is applied.

[0016] The overall thickness of the PDLC film 100A is, for example, 30 μm to 250 μm, preferably 50 μm to 150 μm.

[0017] A-2. Polymer-dispersed liquid crystal layer The PDLC layer 10 comprises a polymer matrix 12 and liquid crystal droplets 14 dispersed within the polymer matrix 12. In the embodiment shown in FIG1 , the liquid crystal droplets 14 contain a photoreactive liquid crystal compound 15 and a non-reactive liquid crystal compound 16 as liquid crystal compounds. From the perspectives of achieving a PDLC film with a large difference between the haze values ​​in the scattering state and the transparent state and lowering the operating voltage, it is preferred that the liquid crystal droplets 14 contain the non-reactive liquid crystal compound 16. However, depending on the intended purpose, the liquid crystal droplets 14 may not contain the non-reactive liquid crystal compound 16.

[0018] The average particle size of the liquid crystal droplets 14 can be, for example, 0.3 μm to 9 μm, preferably 0.4 μm to 8 μm. If the average particle size of the liquid crystal droplets is too small, the following problem may arise: the liquid crystal droplets are smaller than the wavelength of light, so light passes through the liquid crystal droplets without being scattered, resulting in insufficient haze. On the other hand, if the average particle size of the liquid crystal droplets is too large compared to the wavelength of light, the following problem may arise: the liquid crystal droplets are too large compared to the wavelength of light, resulting in insufficient haze. Furthermore, the above average particle size of the liquid crystal droplets is the volume average particle size of the liquid crystal droplets when observed in a direction perpendicular to the main surface of the PDLC film.

[0019] The particle size of the liquid crystal droplets preferably has a relatively narrow particle size distribution. The coefficient of variation (CV) of the particle size of the liquid crystal droplets may be, for example, less than 0.4, preferably less than 0.35, and more preferably less than 0.3. The coefficient of variation can be calculated according to the following formula. CV value = standard deviation of liquid crystal droplet size distribution / average particle size

[0020] The polymer matrix 12 may include any suitable resin. The polymer matrix-forming resin may be appropriately selected based on light transmittance, the refractive index of the liquid crystal compound, adhesion to the substrate, etc. The polymer matrix-forming resin preferably has a refractive index similar to that of the liquid crystal compound.

[0021] Examples of polymer matrix-forming resins include thermoplastic resins such as polyurethane resins, polyvinyl alcohol resins, polyethylene resins, polypropylene resins, and acrylic resins. Thermoplastic resins are preferably water-soluble or water-dispersible resins. Examples of polymer matrix-forming resins include curing resins such as liquid crystal polymers, (meth)acrylic resins, silicone resins, epoxy resins, fluororesins, polyester resins, and polyimide resins. A single polymer matrix-forming resin may be used, or two or more may be used in combination.

[0022] As the photoreactive liquid crystal compound 15, a compound having at least two reversibly photodimerizable functional groups and exhibiting liquid crystal properties is used. The photoreactive liquid crystal compound can be gradually polymerized via a photodimerization reaction to form a liquid crystal polymer. Because this photodimerization reaction is reversible, the resulting liquid crystal polymer can be decomposed (depolymerized) by light irradiation, returning to the photoreactive liquid crystal compound. Furthermore, liquid crystal polymers are typically non-liquid crystal. Therefore, liquid crystal polymers do not experience the temperature-induced transitions to liquid crystal, glass, or crystalline phases that are characteristic of liquid crystal compounds.

[0023] The photoreactive liquid crystal compound is preferably a monomeric compound. The molecular weight of the photoreactive liquid crystal compound is, for example, 5000 or less, preferably 3000 or less, and can be 1500 or less.

[0024] The dielectric anisotropy of the photoreactive liquid crystal compound can be positive or negative. Examples of the photoreactive liquid crystal compound include nematic, smectic, and cholesteric liquid crystal compounds, with nematic liquid crystal compounds being preferred. A single photoreactive liquid crystal compound may be used, or a combination of two or more may be used.

[0025] As the reversible photodimerization functional group, any functional group capable of undergoing a reversible photodimerization reaction can be used, with preferred examples including anthracene, coumarin, cinnamate, stilbene, and thymine groups. Examples of the anthracene, coumarin, cinnamate, stilbene, and thymine groups include the structures shown below. The photoreactive liquid crystal compound may also have two or more photodimerization functional groups. [Chemistry 1]

[0026] In one embodiment, a photoreactive liquid crystal compound comprises a core (e.g., a mesogen) containing one or more ring structures and at least two reversibly photodimerizable groups disposed at its terminals. The core and the photodimerizable groups may be directly bonded or bonded via a spacer. The spacer may be, for example, a divalent linking group comprising an alkylene group having 1 to 8 carbon atoms, an ether bond, an ester bond, an amide bond, or the like. In one embodiment, the spacer may be -O-(C1-C8 alkylene)-O- or -C(O)-O-(C1-C8 alkylene)-O-. The number of photodimerizable groups possessed by the photoreactive liquid crystal compound is two or more, for example, two to four, and preferably two or three. A photoreactive liquid crystal compound having three or more photodimerizable groups can form a liquid crystal polymer having a network structure formed by crosslinking. Therefore, when used in combination with a non-reactive liquid crystal compound, the alignment of the non-reactive liquid crystal compound can be more effectively maintained. The photoreactive liquid crystal compound having three or more photodimerization functional groups can be used in an amount of, for example, 10% to 100% by weight, preferably 30% to 100% by weight, relative to the total amount of the photoreactive liquid crystal compound. Specific examples of the photoreactive liquid crystal compound include the photoreactive liquid crystal monomers described in Japanese Patent Application Laid-Open No. 2008-260846.

[0027] The photoreactive liquid crystal compound typically does not have a polymerizable functional group capable of chain polymerization such as radical polymerization and ionic polymerization.

[0028] As the non-reactive liquid crystal compound 16, a liquid crystal compound that exhibits substantially no reactivity with other liquid crystal compounds can be appropriately selected and used. Non-reactive liquid crystal compounds preferably do not have reactive functional groups (e.g., functional groups capable of chain polymerization or step-wise polymerization). Examples of non-reactive liquid crystal compounds include nematic, smectic, and cholesteric liquid crystal compounds. Nematic liquid crystal compounds are preferred for achieving excellent transparency in a transparent state. A single non-reactive liquid crystal compound may be used, or a combination of two or more may be used.

[0029] 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, cyclohexylbiphenyl compounds, phenylpyridine compounds, cyclohexylpyrimidine compounds, cholesterol compounds, and fluorine compounds.

[0030] The birefringence (Δn=ne-no, ne is the extraordinary refractive index, no is the ordinary refractive index) of the non-reactive liquid crystal compound at a wavelength of 589 nm is, for example, 0.05-0.50, preferably 0.10-0.45.

[0031] The polymer matrix content in the PDLC layer is, for example, 30% to 70% by weight, preferably 35% to 65% by weight, and even more preferably 40% to 60% by weight. Within this range, the polymer matrix content can achieve the following benefits: excellent dimming performance at a moderate operating voltage, high mechanical strength, and prevention of liquid crystal leakage from the edges.

[0032] The weight ratio (weight ratio) of the polymer matrix content to the liquid crystal compound (photoreactive liquid crystal compound, or, if a non-reactive liquid crystal compound is present, both the photoreactive liquid crystal compound and the non-reactive liquid crystal compound) in the PDLC layer is, for example, 30:70 to 70:30, preferably 35:65 to 65:35, and more preferably 40:60 to 60:40. In one embodiment, the content of the photoreactive liquid crystal compound in the PDLC layer is, for example, 1% to 20% by weight, preferably 1.5% to 15% by weight, and more preferably 2% to 10% by weight.

[0033] When a non-reactive liquid crystal compound is present, the weight ratio of the photoreactive liquid crystal compound content to the non-reactive liquid crystal compound content (former:latter) in the PDLC layer is, for example, 1:99-40:60, preferably 2:98-35:75, and more preferably 3:97-30:70.

[0034] The total content ratio of the polymer matrix and the liquid crystal compound (the photoreactive liquid crystal compound, and when a non-reactive liquid crystal compound is present, the photoreactive liquid crystal compound and the non-reactive liquid crystal compound) in the PDLC layer can be, for example, 90% by weight to 99.9% by weight, preferably 95% by weight to 99.9% by weight.

[0035] The PDLC layer may further include any appropriate components as needed. Examples of such optional components include surfactants, leveling agents, crosslinking agents, dispersion stabilizers, and polymerization initiators. The content of these optional components in the PDLC layer may be, for example, 0.1% to 10% by weight, preferably 0.1% to 5% by weight.

[0036] The thickness of the PDLC layer is typically 2 μm to 40 μm, preferably 3 μm to 35 μm, and more preferably 4 μm to 30 μm.

[0037] A-3. First base material The first substrate 20 is a substrate with a transparent electrode layer, comprising a substrate body 22 and a transparent electrode layer 24 disposed on one side thereof (the PDLC layer 10 side). Optionally, the first substrate 20 may include a hard coating on one or both sides of the substrate body 22, or a refractive index adjusting layer between the substrate body 22 and the transparent electrode layer 24.

[0038] The surface resistance of the first substrate is preferably 1 Ω / □ to 1000 Ω / □, more preferably 5 Ω / □ to 300 Ω / □, and further preferably 10 Ω / □ to 200 Ω / □.

[0039] The haze value of the first substrate is preferably 20% or less, more preferably 10% or less, and further preferably 0.1% to 10%.

[0040] The total light transmittance of the first substrate is preferably 40% or higher, more preferably 60% or higher, and even more preferably 80% or higher. The total light transmittance can be measured in accordance with JIS K 7361.

[0041] The substrate body 22 can be formed using any appropriate material. The substrate body is typically a polymer film with a thermoplastic resin as the main component. Examples of thermoplastic resins include: polyester resins; cycloolefin resins such as polybutylene; acrylic resins; polycarbonate resins; cellulose resins, etc. Among them, polyester resins, cycloolefin resins, or acrylic resins are preferred. These resins have excellent transparency, mechanical strength, thermal stability, and waterproof properties. The above-mentioned thermoplastic resins can be used alone or in combination of two or more. In addition, optical films used in polarizing plates, such as low phase difference substrates, high phase difference substrates, phase difference plates, absorption-type polarizing films, and polarization selective reflection films, can also be used as the substrate body.

[0042] The thickness of the 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 substrate to 200 μm or less, the PDLC layer can fully function.

[0043] The total light transmittance of the substrate body is preferably 40% or more, more preferably 60% or more, and further preferably 80% or more.

[0044] The transparent electrode layer 24 can be formed using, for example, a metal oxide such as indium tin oxide (ITO), zinc oxide (ZnO), or tin oxide (SnO2). In this case, the metal oxide can be either amorphous or crystalline. Alternatively, the transparent electrode layer can be formed from metal nanowires such as silver nanowires (AgNWs), carbon nanotubes (CNTs), an organic conductive film, a metal layer, or a laminate thereof. A transparent electrode layer comprising ITO is preferred. A transparent electrode layer comprising ITO has excellent transparency. The transparent electrode layer can be patterned into a desired shape depending on the intended purpose.

[0045] The total light transmittance of the transparent electrode layer is preferably 85% or greater, more preferably 87% or greater, and even more preferably 90% or greater. Using a transparent electrode layer with a total light transmittance within this range allows for a PDLC film with high light transmittance in a transparent state. The higher the total light transmittance, the better, with an upper limit of 99%, for example.

[0046] The thickness of the transparent electrode layer is, for example, greater than 10 nm, preferably greater than 15 nm, and the thickness of the transparent electrode layer is, for example, less than 50 nm, preferably less than 35 nm, and more preferably less than 30 nm.

[0047] The transparent electrode layer is deposited on one surface of the substrate, for example, by sputtering. After the metal oxide layer is formed by sputtering, it can be crystallized by annealing. Annealing can be performed, for example, by heat treating the metal oxide layer at 120°C to 300°C for 10 to 120 minutes.

[0048] The refractive index adjusting layer and the hard coating layer can adopt the structures known in the art, and therefore their detailed structures are omitted.

[0049] A-4. Second base material The second substrate 30 is typically a substrate with a transparent electrode layer, comprising a substrate body 32 and a transparent electrode layer 34 disposed on one side thereof (the PDLC layer 10 side). Optionally, the second substrate 30 may include a hard coating on one or both sides of the substrate body 32, or a refractive index adjusting layer between the substrate body 32 and the transparent electrode layer 34.

[0050] The surface resistance of the second substrate is preferably 1 Ω / □ to 1000 Ω / □, more preferably 5 Ω / □ to 300 Ω / □, and further preferably 10 Ω / □ to 200 Ω / □.

[0051] The haze value of the second substrate is preferably 20% or less, more preferably 10% or less, and further preferably 0.1% to 10%.

[0052] The total light transmittance of the second substrate is preferably 40% or more, more preferably 60% or more, and further preferably 80% or more.

[0053] The substrate body 32 and the transparent electrode layer 34 can be described in the same manner as the substrate body 22 and the transparent electrode layer 24 in the first substrate 20. The second substrate can have the same structure as the first substrate or a different structure.

[0054] A-5. Method for manufacturing polymer dispersed liquid crystal film The PDLC film can be manufactured using any suitable manufacturing method. In one embodiment, the PDLC film manufacturing method includes: preparing a coating liquid containing a polymer matrix-forming resin, a liquid crystal compound (a photoreactive liquid crystal compound, or, if a non-reactive liquid crystal compound is present, both the photoreactive liquid crystal compound and the non-reactive liquid crystal compound), and a dispersion medium; applying the coating liquid to one side of a first substrate to form a coating layer; drying the coating layer to form a polymer matrix from the polymer matrix-forming resin, thereby obtaining a PDLC layer; and laminating a second substrate onto the PDLC layer. The coating liquid is preferably an emulsion coating liquid in which liquid crystal particles containing the liquid crystal compound are dispersed in a dispersion medium. Water or a mixed solvent of water and a water-miscible organic solvent is preferably used as the dispersion medium. Examples of water-miscible organic solvents include C1-3 alcohols, acetone, and DMSO (dimethyl sulfoxide).

[0055] In another embodiment, a method for manufacturing a PDLC film includes preparing a coating liquid containing a curable resin for forming a polymer matrix, a liquid crystal compound (a photoreactive liquid crystal compound, or, if a non-reactive liquid crystal compound is present, both the photoreactive liquid crystal compound and the non-reactive liquid crystal compound), and a polymerization initiator; applying the coating liquid to one side of a first substrate to form a coating layer; laminating a second substrate on the coating layer to form a laminate; and irradiating the laminate with active energy rays to polymerize the curable resin to form a polymer matrix, thereby obtaining a PDLC layer. The coating liquid is preferably in a homogeneous phase, so that the polymer matrix and the liquid crystal compound can undergo phase separation as the curable resin polymerizes. Ultraviolet light is preferably used as the active energy rays. Alternatively, the coating liquid can be filled between the first and second laminated substrates with a spacer interposed therebetween, and then phase separation can be achieved by irradiation with active energy rays.

[0056] A-6. Variations Figure 2 is a schematic cross-sectional view illustrating the structure of a PDLC film according to another embodiment of the present invention. The PDLC film 100B comprises a PDLC layer 10 comprising a polymer matrix 12 and liquid crystal droplets 14 dispersed within the polymer matrix 12. The liquid crystal droplets 14 contain, as liquid crystal compounds, a photoreactive liquid crystal compound 15 having at least two reversibly photodimerizable functional groups and a non-reactive liquid crystal compound 16. The PDLC film 100B comprises a first substrate 20 on one side of the PDLC layer 10 and a second substrate 30 on the other side. The first substrate 20 and the second substrate 30 are respectively composed of substrate bodies 22 and 32 and lack a transparent electrode layer. The PDLC film 100B having this structure is preferably used, for example, as a diffusion film. The same descriptions as above apply to the PDLC layer 10 and substrate bodies 22 and 32. The PDLC film 100B can be manufactured using the same method as described in Section A-5.

[0057] B. How to use polymer dispersed liquid crystal film According to another aspect of the present invention, a method for using the PDLC film described in item A is provided. The method for using the PDLC film according to the embodiment of the present invention includes: a fixing step of forming a liquid crystal polymer by photodimerization of the photoreactive liquid crystal compound; and The resetting step generates the photoreactive liquid crystal compound by depolymerization of the liquid crystal polymer. In the method for using a PDLC film according to an embodiment of the present invention, the fixing step may be performed again after the resetting step. Furthermore, the fixing and resetting steps may be repeated. The number of repetitions is not limited, as long as the effects of the present invention are achieved. The region where the liquid crystal polymer is grown in the second and subsequent fixing steps may be different from the region where the liquid crystal polymer was grown in the previous fixing steps. According to the method for using a PDLC film according to an embodiment of the present invention, the PDLC film described in Section A can be used as a rewritable PDLC film. The method for using a PDLC film according to one embodiment of the present invention is described in detail below with reference to FIG. 3 .

[0058] First, as shown in FIG3(a), a PDLC film 100A is prepared. The PDLC film 100A comprises a PDLC layer 10 comprising a polymer matrix 12 and liquid crystal droplets 14 dispersed within the polymer matrix 12, as well as a first substrate 20 and a second substrate 30 disposed on either side of the PDLC layer 10. The liquid crystal droplets 14 contain a photoreactive liquid crystal compound 15 having at least two reversible photodimerization functional groups. Within the PDLC film 100A, the liquid crystal droplets 14 further contain a non-reactive liquid crystal compound 16.

[0059] In the first fixing step, the PDLC film 100A is irradiated with light to induce a photodimerization reaction of the photoreactive liquid crystal compound 15 (Figure 3(b)). This gradually polymerizes the photoreactive liquid crystal compound 15, forming a liquid crystal polymer 17 (Figure 3(c)). In the illustrated example, the PDLC layer 10 is irradiated with light while a voltage is applied and through a photomask 200 with a predetermined pattern. This allows the photoreactive liquid crystal compound 15 in the irradiated area to polymerize while aligned in the direction of the electric field. The resulting liquid crystal polymer 17 is non-liquid crystal and does not respond to the electric field. Therefore, the liquid crystal polymer 17 is fixed while aligned in the thickness direction. Within the same liquid crystal droplet 14, the non-reactive liquid crystal compound 16 is constrained by the alignment of the liquid crystal polymer 17. As a result, the irradiated area remains transparent with minimal haze, regardless of whether a voltage is applied or not. On the other hand, in the non-irradiated areas, the photodimerization reaction of the photoreactive liquid crystal compound 15 does not occur, and thus the liquid crystal polymer 17 is not formed. The refractive index of the liquid crystal droplets 14 can change depending on the applied voltage. As a result, the non-irradiated areas can be in a scattering state with a high haze when no voltage is applied, and the haze decreases and becomes transparent when a voltage is applied. Therefore, according to the above fixing step, by using a mask corresponding to the target pattern, a first area (irradiated area) and a second area (non-irradiated area) can be formed in a desired pattern, with different haze changes between the applied and unapplied voltage states. The haze change in the first area between the applied and unapplied voltage states is smaller than the haze change in the second area.

[0060] The light irradiation conditions in the fixing step can be any conditions that induce a photodimerization reaction of the photoreactive liquid crystal compound. The irradiation conditions, such as the wavelength, irradiation time, and irradiation temperature, can be appropriately set depending on the type of photoreactive liquid crystal compound. When using a photoreactive liquid crystal compound having an anthracene group as a photodimerization functional group, the peak wavelength of the irradiation light can be set, for example, to 315 nm to 400 nm, or, for example, to 330 nm to 380 nm. The exposure dose can be set, for example, to 10 J / m² to 10,000 J / m², or, for example, to 100 J / m² to 5,000 J / m². The irradiation temperature can be set, for example, to -20°C to 80°C, or, for example, to -20°C to 60°C.

[0061] Next, in the reset step, the PDLC film 100A is irradiated with light to cause a depolymerization reaction of the liquid crystal polymer 17 (Figure 3(d)). This decomposes the liquid crystal polymer 17, generating a photoreactive liquid crystal compound 15 (Figure 3(e)). In the illustrated example, the entire surface of the PDLC film 100A is irradiated with light, but irradiation may also be performed on only the irradiated area. This reset step erases the pattern applied to the PDLC film 100A. In the illustrated example, the pattern is completely erased, returning to its original state, but a partial depolymerization of the liquid crystal polymer may also be performed to soften the pattern (reduce the haze difference of the pattern). Furthermore, light irradiation can be performed while voltage is applied.

[0062] The light irradiation conditions in the resetting step can be any conditions that induce a depolymerization reaction of the liquid crystal polymer. The irradiation conditions, such as the wavelength, irradiation time, and irradiation temperature, can be appropriately set depending on the type of photoreactive liquid crystal compound. The peak wavelength of the irradiation light in the resetting step can be shorter than the peak wavelength of the irradiation light in the fixing step. When using a photoreactive liquid crystal compound having an anthracene group as a photodimerization functional group, the peak wavelength of the irradiation light can be set, for example, to 230 nm to 290 nm, or, for example, to 240 nm to 290 nm. The exposure dose can be set, for example, to 10 J / m² to 10,000 J / m², or, for example, to 100 J / m² to 5,000 J / m². The irradiation temperature can be set, for example, to -20°C to 80°C, or, for example, to -20°C to 60°C.

[0063] If necessary, a fixing step can be performed again after the reset step. Specifically, the PDLC film 100A after the reset step can be irradiated with light to induce a photodimerization reaction of the photoreactive liquid crystal compound 15. This allows the photoreactive liquid crystal compound 15 to gradually polymerize, forming the liquid crystal polymer 17 (a second fixing step). In this case, by irradiating with light using a mask with a different intervening pattern than that used in the first fixing step, a PDLC film having first and second regions can be obtained with a pattern different from that applied in the first fixing step.

[0064] If necessary, a reset step (second reset step) can be performed again after the second fixing step. The pattern applied during the second fixing step can be eliminated by the second reset step. Similar to the first reset step, the pattern can be completely eliminated or reduced (the haze difference of the pattern is reduced).

[0065] As described above, by repeating the fixing step and the resetting step, the design (pattern) applied to the PDLC film 100A can be rewritten and changed to any design.

[0066] In the embodiment shown in Figure 3, during the fixing step, the photodimerization reaction of the photoreactive liquid crystal compound occurs while voltage is applied. Alternatively, as shown in Figure 4, the photodimerization reaction can occur without voltage (Figure 4(b)). In this case, the photoreactive liquid crystal compound 15 in the irradiated area polymerizes and fixes in a non-aligned state, while the photoreactive liquid crystal compound 15 in the non-irradiated area does not undergo photodimerization. As a result, the irradiated area (first area) exhibits a scattering state with high haze in both the voltage-applied and non-voltage-applied states. The non-irradiated area (second area) exhibits a scattering state with high haze in the non-voltage-applied state, and the haze decreases with voltage application, resulting in a transparent state. The change in haze between the voltage-applied and non-voltage-applied states in the first area (irradiated area) is smaller than the change in haze in the second area (non-irradiated area).

[0067] The above-described method for using a PDLC film can advantageously produce a patterned PDLC film having first and second regions formed in a predetermined pattern, each with a different haze variation between the voltage-applied and voltage-unapplied states. Therefore, the method for using a PDLC film described in Section B can be a method for producing a patterned PDLC film. The pattern applied to the patterned PDLC film according to embodiments of the present invention can be reversibly altered.

[0068] The PDLC film usage method according to the embodiments of the present invention can also be applied to a PDLC film (diffusion film) 100B whose substrate does not have a transparent electrode layer. For example, as shown in Figure 5 , by alternately repeating the aforementioned fixing and resetting steps on the PDLC film 100B, low-haze regions and high-haze regions of the PDLC film 100B can be formed in different patterns (pattern A and pattern B in the example shown). In this case, applying a voltage to the PDLC layer during the fixing step can be performed by placing separately prepared electrodes on the surfaces of the first and second substrates and applying the voltage. Example

[0069] The present invention is further described below using examples, but the present invention is not limited by these examples. The measurement methods for various properties are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

[0070] (1) Thickness The measurement was performed using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C"). (2) Volume average particle size of liquid crystal particles in liquid crystal emulsion To 200 ml of an aqueous electrolyte solution ("ISOTON II" manufactured by Coulter), 0.1% by weight of the liquid crystal emulsion was added. The resulting mixture was used as the measurement sample. Using a Multisizer 3 (manufactured by Coulter, 20 μm aperture), the volume of each discretized particle size was counted, divided into 256 equal intervals from 0.4 μm to 12 μm on a logarithmic basis. The volume average particle size was calculated by counting the volume of each discretized particle size. Furthermore, in the case of particles larger than 12 μm, the aperture was set to 30 μm, and the volume average particle size was calculated by counting the volume of each discretized particle size, divided into 256 equal intervals from 0.6 μm to 18 μm on a logarithmic basis. (3) Average particle size of resin particles A sample was prepared by adding a few drops of the resin dispersion to 100 mL of water. Using a dynamic light scattering particle size distribution analyzer (Microtrac, Nanotrac 150), the sample was placed in the measuring rack and the measurement was performed after confirming a measurable concentration on the monitor. (4) Haze The haze was measured using a haze meter (manufactured by Nippon Denshoku Co., Ltd., product name "NDH4000") in accordance with JIS K 7136.

[0071] [Example 1] (First substrate and second substrate) An ITO layer was formed on one surface of a PET substrate (thickness: 50 μm) by sputtering, thereby obtaining a substrate having a structure of [substrate body / transparent electrode layer].

[0072] (Preparation of coating solution) A liquid crystal emulsion was prepared by mixing 2.5 parts of the photoreactive liquid crystal compound A shown below, 47 parts of a non-reactive liquid crystal compound (JNC Corporation, product name "LX-153XX," birefringence Δn = 0.149), 49.5 parts of pure water, and 1.0 part of a surfactant (Daiichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") and treating with a homogenizer. The resulting liquid crystal emulsion had an average particle size of 3.5 μm. 47.6 parts of the above-mentioned liquid crystal emulsion, 32 parts of a polyether polyurethane resin aqueous dispersion (manufactured by DSM, trade name "NeoRez R967", polymer average particle size: 80 nm, CV value = 0.27, solid content: 40 wt%), 0.1 part of a leveling agent (manufactured by DIC Corporation, product name "F-444"), 1 part of a crosslinking agent (tris[3-(2-methylaziridin-1-yl)propionate = propyltrimethylol]), and 19.3 parts of pure water were mixed to obtain an emulsion coating liquid. [Chemistry 2]

[0073] (Production of PDLC film) The emulsion coating liquid was applied to the surface of the ITO layer of the first substrate and dried at 40°C to form a 10 μm thick PDLC layer. Subsequently, a laminating machine was used to apply a lamination pressure of 0.4 MPa / m while laminating the second substrate onto the PDLC layer, with the ITO layer and PDLC layer facing each other. This resulted in a PDLC film with a structure of [first substrate / PDLC layer / second substrate].

[0074] [Example 2] A PDLC film was obtained in the same manner as in Example 1 except that 1.25 parts of the photoreactive liquid crystal compound B and 1.25 parts of the photoreactive liquid crystal compound C shown below were used instead of 2.5 parts of the photoreactive liquid crystal compound A. [Chemistry 3]

[0075] [Comparative Example 1] A liquid crystal emulsion was prepared by mixing 44.3 parts of a non-reactive liquid crystal compound (JNC, product name "LX-153XX," birefringence Δn = 0.149), 4.9 parts of a polymerizable liquid crystal compound (BASF, product name "PALIOCOLOR LC-242"), 0.3 parts of a photopolymerization initiator (IGM, product name "OMNIRAD 651"), 49.5 parts of pure water, and 1.0 part of a surfactant (Daiichi Kogyo Seiyaku Co., Ltd., product name "Noigen ET159") and treating with a homogenizer. The resulting liquid crystal emulsion had an average particle size of 3.5 μm. A PDLC film was obtained in the same manner as in Example 1 except that the liquid crystal emulsion obtained as above was used.

[0076] The PDLC films obtained in the above Examples and Comparative Examples were subjected to the following fixing step, followed by the following resetting step 1 or 2. The PDLC films subjected to resetting step 2 were subjected to the following fixing step again. Furthermore, the PDLC films after the fixing step were not subjected to the resetting step and were left at room temperature as a control sample. [Fixed steps] The PDLC film was irradiated with light (10 mW / m2) with a peak wavelength of 365 nm for 10 minutes at a temperature of 25°C and an AC voltage of 50 V applied to the PDLC layer. [Reset Step 1] The PDLC film after the fixing step was irradiated with light having a peak wavelength of 280 nm (10 mW / m 2 ) for 30 minutes. [Reset Step 2] The PDLC film after the fixing step was irradiated with light having a peak wavelength of 265 nm (10 mW / m 2 ) for 30 minutes.

[0077] FIG6 shows the change in haze when a voltage of 0 V to 50 V is applied to the PDLC films of Example 1 and Example 2 in the initial state (before the fixing step) and after the fixing step.

[0078] The haze of each PDLC film in the initial state and in each step without voltage application is shown in Table 1 and Figure 7. Furthermore, Table 1 shows the haze of the PDLC film subjected to the reset step 2 without voltage application. [Table 1] Example 1 Example 2 Comparative Example 1 Initial state (Before the fixation step) 86.0 87.1 88.7 Fixed step end time point 51.3 29.7 9.2 Reset steps (10 minutes of irradiation) 64.4 36.1 9.2 Reset steps (20 minutes of irradiation) 69.6 35.9 9.2 Reset steps (30 minutes of irradiation) 73.5 35.9 9.2 End time of the second fixed step 51.9 23.0 9.2

[0079] As shown in Table 1 and Figures 6 and 7, in the PDLC film of the Example, by performing a fixation step while voltage is applied, a region with a low haze is formed even when no voltage is applied. By performing a reset step after the fixation step, the haze in this region in the no-voltage state is restored (increased). Furthermore, by performing a second fixation step while voltage is applied, a region with a low haze is again formed in the no-voltage state. On the other hand, in the PDLC film of the Comparative Example, by performing a fixation step while voltage is applied, a region with a low haze is formed even when no voltage is applied, but even performing a reset step does not restore the haze in this region in the no-voltage state. [Industrial Applicability]

[0080] The PDLC film of the present invention is suitable for various applications such as displays such as advertisements and guide plates, and smart windows.

[0081] 10: PDLC layer 12:Polymer Matrix 14:LCD droplets 15: Photoreactive liquid crystal compound 16: Non-reactive liquid crystal compound 17: Liquid Crystal Polymer 20: 1st base material 22:Substrate body 24: Transparent electrode layer 30: Second base material 32:Substrate body 34: Transparent electrode layer 100:PDLC film 100A:PDLC film 100B:PDLC film 200: Mask

Claims

1. A polymer-dispersed liquid crystal film having a polymer-dispersed liquid crystal layer comprising a polymer matrix and droplets, wherein the droplets are dispersed in the polymer matrix and comprise a liquid crystal compound, and the liquid crystal compound comprises a photoreactive liquid crystal compound having at least two reversible photodimeric functional groups.

2. The polymer-dispersed liquid crystal film of claim 1, wherein the liquid crystal compound further comprises a non-reactive liquid crystal compound.

3. The polymeric dispersion liquid crystal film of claim 1, wherein the reversible photodimer functional group is selected from anthracene, coumarin, cinnamic acid, styrannyl and thymine.

4. The polymer-dispersed liquid crystal film of claim 1, wherein the photoreactive liquid crystal compound comprises a photoreactive liquid crystal compound having three or more of the aforementioned reversible photodimer functional groups.

5. The polymer-dispersed liquid crystal film of claim 1, further comprising a substrate with transparent electrode layers disposed on both sides of the polymer-dispersed liquid crystal layer.

6. The polymer-dispersed liquid crystal film of claim 5, which can change the amount of haze change between the voltage-applied state and the voltage-unapplied state by means of the reversible photodimerization reaction of the above-mentioned photoreactive liquid crystal compound.

7. A method of using a polymer-dispersed liquid crystal film, comprising the method of using the polymer-dispersed liquid crystal film as described in claim 1, and including: The process includes a fixed step in which a liquid crystal polymer is generated by photodimerization of the aforementioned photoreactive liquid crystal compound; and a reset step in which the aforementioned photoreactive liquid crystal compound is generated by depolymerization of the aforementioned liquid crystal polymer.

8. The method of using the polymer-dispersed liquid crystal film as described in claim 7, wherein the above-mentioned fixing step is performed again after the above-mentioned reset step.

9. The method of using the polymer-dispersed liquid crystal film as described in claim 7, wherein the above-described fixing step and the above-described resetting step are performed repeatedly.

10. The method of using the polymer-dispersed liquid crystal film as claimed in claim 8 or 9, wherein the region where the liquid crystal polymer is formed in subsequent fixing steps is different from the region where the liquid crystal polymer is formed in previous fixing steps.

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