Polymer dispersed liquid crystal film and method for using same

Abstract

Provided is a polymer dispersed liquid crystal film wherein a temporarily applied design can be changed. This polymer dispersed liquid crystal film has a polymer dispersed liquid crystal layer including a polymer matrix and droplets that are dispersed in the polymer matrix and include a liquid crystal compound. The liquid crystal compound includes a photoreactive liquid crystal compound that has at least two reversible photodimerization functional groups.

Description

Polymer-dispersed liquid crystal film and method of use thereof

[0001] The present invention relates to polymer dispersed liquid crystal films and methods of using polymer dispersed liquid crystal films.

[0002] A PDLC film having a polymer dispersed liquid crystal (hereinafter sometimes referred to as "PDLC") layer containing a polymer matrix and droplets of a liquid crystal compound between a pair of transparent electrode layers can change the degree of scattering of transmitted light through the PDLC layer depending on the amount of applied voltage. For example, a PDLC film can switch between a light scattering state (scattering state) and a light transmitting state (transparent state) by switching between an applied voltage state and an unapplied voltage state (Patent Document 1). Taking advantage of this function, PDLC films are being considered for application to displays such as advertisements and guide signs, smart windows, and the like.

[0003] Japanese Patent Application Laid-Open No. 2002-189123

[0004] The present inventors have discovered that a PDLC film can be fabricated using a polymerizable liquid crystal compound and then polymerized in a desired region to impart a desired design to the PDLC film. This method allows the production of a PDLC film with a desired design, but the design once applied is irreversible and cannot be changed to another design.

[0005] A primary object of the present invention is to provide a PDLC film that allows for the modification of a design once applied.

[0006] [1] According to one aspect of the present invention, there is provided a polymer-dispersed liquid crystal film having a polymer-dispersed liquid crystal layer including a polymer matrix and droplets containing a liquid crystal compound dispersed in the polymer matrix, the liquid crystal compound comprising 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 comprise a non-reactive liquid crystal compound. [3] In the polymer-dispersed liquid crystal film described in [1] or [2] above, the reversible photodimerization functional groups may be selected from an anthracene group, a coumarin group, a cinnamic acid group, a stilbene group, and a thymine group. [4] In the polymer-dispersed liquid crystal film described in any one of [1] to [3] above, the photoreactive liquid crystal compound may comprise a photoreactive liquid crystal compound having three or more reversible photodimerization functional groups. [5] In the polymer-dispersed liquid crystal film described in any one of [1] to [4] above, the film may further comprise substrates with transparent electrode layers disposed on both sides of the polymer-dispersed liquid crystal layer. [6] In the polymer dispersed liquid crystal film according to any one of [1] to [5] above, the amount of change in haze between a voltage applied state and a voltage not applied state may be variable by a reversible photodimerization reaction of the photoreactive liquid crystal compound. [7] According to another aspect of the present invention, there is provided a method for using the polymer dispersed liquid crystal film according to any one of [1] to [6] above, the method comprising: a fixation step of generating a liquid crystal polymer by a photodimerization reaction of the photoreactive liquid crystal compound; and a resetting step of generating the photoreactive liquid crystal compound by a depolymerization reaction of the liquid crystal polymer. [8] In the method for using the polymer dispersed liquid crystal film according to [7] above, the fixation step may be performed again after the resetting step. [9] In the method for using the polymer dispersed liquid crystal film according to [7] or [8] above, the fixation step and the resetting step may be repeated.

[10] In the method for using the polymer dispersed liquid crystal film according to the above [8] or [9], the region where the liquid crystal polymer is produced in the second or subsequent fixing step may be different from the region where the liquid crystal polymer is produced in the previous fixing step.

[0007] According to an embodiment of the present invention, a PDLC film is provided in which a design that has already been applied can be changed by using a photoreactive liquid crystal compound having a reversible photodimerization functional group as the liquid crystal compound.

[0008] FIG. 1 is a schematic cross-sectional view illustrating the configuration of a PDLC film according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating the configuration of a PDLC film according to another embodiment of the present invention. FIG. 3 is a schematic view illustrating a method of using a PDLC film according to one embodiment of the present invention. FIG. 4 is a schematic view illustrating a method of using a PDLC film according to another embodiment of the present invention. FIG. 5 is a graph showing the change in haze when a voltage is applied to a PDLC film of an example. FIG. 6 is a graph showing the haze of a PDLC film of an example in each process when no voltage is applied.

[0009] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In this specification, the term "to" indicating a range of values ​​includes the upper and lower limits.

[0010] A. Polymer-Dispersed Liquid Crystal Film According to one aspect of the present invention, a PDLC film is provided, which has a PDLC layer including a polymer matrix and droplets containing a liquid crystal compound dispersed in the polymer matrix, the liquid crystal compound comprising a photoreactive liquid crystal compound having at least two reversible photodimerization functional groups. The photoreactive liquid crystal compound can be sequentially polymerized by a photodimerization reaction to produce a liquid crystal polymer. The resulting liquid crystal polymer can then be decomposed by a depolymerization reaction to produce a photoreactive liquid crystal compound (i.e., return to the photoreactive liquid crystal compound). Because these reactions are reversible, PDLC films according to embodiments of the present invention can utilize the polymerization and depolymerization of the photoreactive liquid crystal compound to arbitrarily form regions of different haze or haze change, thereby achieving desired designs. Furthermore, designs that have already been applied can be changed. Therefore, PDLC films according to embodiments of the present invention can be used, for example, as rewritable light control films or diffusion films.

[0011] A-1. Overall Configuration of PDLC Film FIG. 1 is a schematic cross-sectional view illustrating the configuration of a PDLC film according to one embodiment of the present invention. PDLC film 100A has a PDLC layer 10 including a polymer matrix 12 and droplets 14 of a liquid crystal compound (hereinafter, sometimes referred to as "liquid crystal droplets") dispersed in the polymer matrix 12. The liquid crystal droplets 14 contain, as liquid crystal compounds, a photoreactive liquid crystal compound 15 having at least two reversible photodimerization functional groups and a non-reactive liquid crystal compound 16. PDLC film 100A has a first substrate 20 on one side of PDLC layer 10 and a second substrate 30 on the other side. The first substrate 20 and second substrate 30 each have a substrate body 22, 32 and a transparent electrode layer 24, 34, respectively.

[0012] The PDLC film 100A shown in FIG. 1 is in the normal mode. Specifically, as shown in FIG. 1( a), in the absence of applied voltage, the photoreactive liquid crystal compounds 15 and nonreactive liquid crystal compounds 16 in the liquid crystal droplets 14 are not oriented, and scattering occurs due to the difference in refractive index between the polymer matrix 12 and the liquid crystal droplets 14, resulting in a scattered state. On the other hand, as shown in FIG. 1( b), in the presence of applied voltage, the photoreactive liquid crystal compounds 15 and nonreactive liquid crystal compounds 16 are oriented along the electric field direction, and the refractive index of the liquid crystal droplets 14 matches that of the polymer matrix 12, resulting in a transparent state with a lower haze than the scattered state. Unlike the illustrated example, the PDLC film according to an embodiment of the present invention may be in the reverse mode, in which the PDLC film is in the scattered state in the presence of applied voltage and in a transparent state with a lower haze than the scattered state in the absence of applied voltage.

[0013] As will be described in detail in Section B, the PDLC film 100A is typically capable of changing the amount of change in haze between the applied and unapplied voltage states by the reversible photodimerization reaction of the photoreactive liquid crystal compound 15. Specifically, the amount of change in haze between the applied and unapplied voltage states can be reduced by sequentially polymerizing the photoreactive liquid crystal compound through photodimerization, and the amount of change in haze can be restored by depolymerizing the compound.

[0014] The voltage applied to the PDLC film 100A in the voltage-applied state is a voltage (operating voltage) that can operate the PDLC film 100A, and may be, for example, 5 V to 200 V, and preferably 10 V to 100 V. In this specification, the term "voltage-applied state" refers to a state in which an operating voltage is applied to the PDLC film, and may be, for example, a state in which a voltage of 50 V is applied.

[0015] The total thickness of the PDLC film 100A is, for example, 30 μm to 250 μm, and preferably 50 μm to 150 μm.

[0016] A-2. Polymer-Dispersed Liquid Crystal Layer The PDLC layer 10 includes a polymer matrix 12 and liquid crystal droplets 14 dispersed in the polymer matrix 12. In the embodiment shown in Fig. 1, the liquid crystal droplets 14 include, as liquid crystal compounds, a photoreactive liquid crystal compound 15 and a nonreactive liquid crystal compound 16. From the viewpoints of obtaining a PDLC film with a large difference in haze between the scattering state and the transparent state, reducing the operating voltage, and the like, it is preferable that the liquid crystal droplets 14 include the nonreactive liquid crystal compound 16; however, depending on the purpose, the liquid crystal droplets 14 do not necessarily need to include the nonreactive liquid crystal compound 16.

[0017] The average particle diameter 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 diameter of the liquid crystal droplets is too small, the liquid crystal droplets are smaller than the wavelength of light, so light passes through the liquid crystal droplets without scattering, which can result in a problem of insufficient haze being obtained. On the other hand, if the average particle diameter of the liquid crystal droplets is too large, the liquid crystal droplets are too large compared to the wavelength of light, which can result in a problem of insufficient haze being obtained. Note that the above average particle diameter of the liquid crystal droplets is the volume-average particle diameter of the liquid crystal droplets when viewed from a direction perpendicular to the main surface of the PDLC film.

[0018] The particle diameter of the liquid crystal droplets preferably has a relatively narrow particle size distribution. The coefficient of variation (CV value) of the particle diameter of the liquid crystal droplets may be, for example, less than 0.4, preferably 0.35 or less, and more preferably 0.3 or less. The coefficient of variation can be calculated using the following formula: CV value = standard deviation of particle diameter distribution of liquid crystal droplets / average particle diameter

[0019] The polymer matrix 12 may be made of any appropriate resin. The resin for forming the polymer matrix may be appropriately selected depending on the light transmittance, the refractive index of the liquid crystal compound, the adhesion to the substrate, etc. The resin for forming the polymer matrix preferably has a refractive index similar to that of the liquid crystal compound.

[0020] Examples of the polymer matrix-forming resin include thermoplastic resins such as urethane resins, polyvinyl alcohol resins, polyethylene resins, polypropylene resins, and acrylic resins. The thermoplastic resin is preferably a water-soluble resin or a water-dispersible resin. Examples of the polymer matrix-forming resin include curable resins such as liquid crystal polymers, (meth)acrylic resins, silicone resins, epoxy resins, fluorine-containing resins, polyester resins, and polyimide resins. Only one type of polymer matrix-forming resin may be used, or two or more types may be used in combination.

[0021] The photoreactive liquid crystal compound 15 is a compound having at least two reversible photodimerization functional groups and exhibiting liquid crystallinity. The photoreactive liquid crystal compound can undergo sequential polymerization through a photodimerization reaction to produce a liquid crystal polymer. Because the photodimerization reaction is reversible, the produced liquid crystal polymer can be decomposed (depolymerized) by light irradiation and return to the photoreactive liquid crystal compound. Note that liquid crystal polymers are typically non-liquid crystals. Therefore, in liquid crystal polymers, for example, the transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is unique to liquid crystal compounds, does not occur.

[0022] The photoreactive liquid crystal compound is preferably a monomer compound. The molecular weight of the photoreactive liquid crystal compound is, for example, 5,000 or less, preferably 3,000 or less, and may be 1,500 or less.

[0023] The dielectric anisotropy of the photoreactive liquid crystal compound may be positive or negative. The photoreactive liquid crystal compound may be, for example, a nematic, smectic, or cholesteric liquid crystal compound, and preferably a nematic liquid crystal compound. The photoreactive liquid crystal compound may be used alone or in combination of two or more.

[0024] The reversible photodimerization functional group can be any functional group capable of causing a reversible photodimerization reaction, and preferred examples thereof include an anthracene group, a coumarin group, a cinnamic acid group, a stilbene group, and a thymine group. The anthracene group, the coumarin group, the cinnamic acid group, the stilbene group, and the thymine group can have, for example, the structure shown below. The photoreactive liquid crystal compound may have two or more types of photodimerization functional groups.

[0025] In one embodiment, the photoreactive liquid crystal compound has a core (e.g., a mesogenic portion) containing one or more ring structures and at least two reversible photodimerization functional groups located at its terminals. The core and the photodimerization functional groups may be bonded directly or via a spacer. The spacer may be, for example, a divalent linking group containing 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 photodimerization functional groups contained in the photoreactive liquid crystal compound may be two or more, for example, 2 to 4, preferably 2 or 3. A photoreactive liquid crystal compound having three or more photodimerization functional groups can produce a liquid crystal polymer having a crosslinked network structure, and therefore, when used in combination with a nonreactive liquid crystal compound, can more effectively maintain the alignment of the nonreactive liquid crystal compound. The photoreactive liquid crystal compound having three or more photodimerizable functional groups can be used in an amount of, for example, 10% by weight to 100% by weight, preferably 30% by weight to 100% by weight, based on the total amount of the photoreactive liquid crystal compound. Specific examples of the photoreactive liquid crystal compound include photoreactive liquid crystalline monomers described in JP-A-2008-260846.

[0026] The photoreactive liquid crystal compound typically does not have a polymerizable functional group capable of chain polymerization such as radical polymerization or ionic polymerization.

[0027] As the non-reactive liquid crystal compound 16, a liquid crystal compound that is substantially non-reactive with other liquid crystal compounds can be appropriately selected and used. The non-reactive liquid crystal compound preferably does not have a reactive functional group (e.g., a functional group capable of chain polymerization or sequential polymerization). The non-reactive liquid crystal compound may be, for example, a nematic, smectic, or cholesteric liquid crystal compound. It is preferable to use a nematic liquid crystal compound because it can achieve excellent transparency in the transparent state. The non-reactive liquid crystal compound may be used alone or in combination of two or more types.

[0028] Examples of nematic liquid crystal compounds include biphenyl-based compounds, phenylbenzoate-based compounds, cyclohexylbenzene-based compounds, azoxybenzene-based compounds, azobenzene-based compounds, azomethine-based compounds, terphenyl-based compounds, biphenylbenzoate-based compounds, cyclohexylbiphenyl-based compounds, phenylpyridine-based compounds, cyclohexylpyrimidine-based compounds, cholesterol-based compounds, and fluorine-based compounds.

[0029] 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 to 0.50, preferably 0.10 to 0.45.

[0030] The polymer matrix content in the PDLC layer is, for example, 30 to 70% by weight, preferably 35 to 65% by weight, and more preferably 40 to 60% by weight. When the polymer matrix content is within this range, it is possible to obtain effects such as a good light control function at a moderate operating voltage, good mechanical strength, and prevention of liquid crystal leakage from the edges.

[0031] The weight ratio (former:latter) of the content of the polymer matrix to the content of the liquid crystal compounds (photoreactive liquid crystal compound and nonreactive liquid crystal compound, if present) 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.

[0032] When a non-reactive liquid crystal compound is present, the weight ratio of the content of the photoreactive liquid crystal compound to the content of the non-reactive liquid crystal compound in the PDLC layer (former:latter) is, for example, 1:99 to 40:60, preferably 2:98 to 35:75, and more preferably 3:97 to 30:70.

[0033] The total content of the polymer matrix and the liquid crystal compounds (photoreactive liquid crystal compounds and nonreactive liquid crystal compounds, if present) in the PDLC layer may be, for example, 90% by weight to 99.9% by weight, preferably 95% by weight to 99.9% by weight.

[0034] The PDLC layer may further contain any appropriate component, as necessary. Such optional components include a surfactant, a leveling agent, a crosslinking agent, a dispersion stabilizer, a polymerization initiator, etc. The content of the optional component in the PDLC layer may be, for example, 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

[0035] 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.

[0036] A-3. First Substrate The first substrate 20 is a substrate with a transparent electrode layer, which has a substrate body 22 and a transparent electrode layer 24 provided on one side (the PDLC layer 10 side) of the substrate body 22. The first substrate 20 may have a hard coat layer on one or both sides of the substrate body 22, as necessary, and may also have a refractive index adjustment layer between the substrate body 22 and the transparent electrode layer 24.

[0037] The surface resistance value of the first substrate is preferably 1 Ω / □ to 1000 Ω / □, more preferably 5 Ω / □ to 300 Ω / □, and even more preferably 10 Ω / □ to 200 Ω / □.

[0038] The haze value of the first substrate is preferably 20% or less, more preferably 10% or less, and even more preferably 0.1% to 10%.

[0039] The total light transmittance of the first substrate is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more. The total light transmittance can be measured in accordance with JIS K 7361.

[0040] The substrate body 22 can be formed using any appropriate material. Typically, the substrate body is a polymer film primarily composed of a thermoplastic resin. Examples of thermoplastic resins include polyester-based resins; cycloolefin-based resins such as polynorbornene; acrylic resins; polycarbonate-based resins; and cellulose-based resins. Among these, polyester-based resins, cycloolefin-based resins, and acrylic resins are preferred. These resins are excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, and the like. The above-mentioned thermoplastic resins may be used alone or in combination of two or more. Optical films used in polarizing plates, such as low-retardation substrates, high-retardation substrates, retardation plates, absorptive polarizing films, and polarized light selective reflection films, can also be used as the substrate body.

[0041] The thickness of the substrate body is preferably 200 μm or less, more preferably 3 μm to 100 μm, and even more preferably 5 μm to 70 μm. By keeping the thickness of the substrate body 200 μm or less, the function of the PDLC layer can be fully exhibited.

[0042] The total light transmittance of the substrate body is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more.

[0043] The transparent electrode layer 24 may be made of, for example, indium tin oxide (ITO), zinc oxide (ZnO), or tin oxide (SnO ２The transparent electrode layer may be formed using a metal oxide such as ZnO. In this case, the metal oxide may be an amorphous metal oxide or a crystallized metal oxide. The transparent electrode layer may also be formed using metal nanowires such as silver nanowires (AgNW), carbon nanotubes (CNT), an organic conductive film, a metal layer, or a laminate thereof. Preferably, a transparent electrode layer containing ITO is formed. A transparent electrode layer containing ITO has excellent transparency. The transparent electrode layer may be patterned into a desired shape depending on the purpose.

[0044] The total light transmittance of the transparent electrode layer is preferably 85% or more, more preferably 87% or more, and even more preferably 90% or more. By using a transparent electrode layer having a total light transmittance in this range, a PDLC film having high light transmittance in the transparent state can be obtained. The higher the total light transmittance, the more preferable it is, and the upper limit is, for example, 99%.

[0045] The transparent electrode layer has a thickness of, for example, 10 nm or more, preferably 15 nm or more, and for example, 50 nm or less, preferably 35 nm or less, more preferably 30 nm or less.

[0046] The transparent electrode layer is formed on one surface of the substrate body by, for example, sputtering. After forming the metal oxide layer by sputtering, it can be crystallized by annealing. Annealing is performed by heat treatment at 120°C to 300°C for 10 to 120 minutes, for example.

[0047] The refractive index adjusting layer and the hard coat layer may have a structure well known in the art, and therefore detailed description of their structures will be omitted.

[0048] A-4. Second Substrate The second substrate 30 is typically a substrate with a transparent electrode layer, which has a substrate body 32 and a transparent electrode layer 34 provided on one side (the PDLC layer 10 side) of the substrate body 32. The second substrate 30 may have a hard coat layer on one or both sides of the substrate body 32, as needed, and may also have a refractive index adjustment layer between the substrate body 32 and the transparent electrode layer 34.

[0049] The surface resistance value of the second substrate is preferably 1 Ω / □ to 1000 Ω / □, more preferably 5 Ω / □ to 300 Ω / □, and even more preferably 10 Ω / □ to 200 Ω / □.

[0050] The haze value of the second substrate is preferably 20% or less, more preferably 10% or less, and even more preferably 0.1% to 10%.

[0051] The total light transmittance of the second substrate is preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more.

[0052] The same explanations as for the substrate body 22 and the transparent electrode layer 24 in the first substrate 20 can be applied to the substrate body 32 and the transparent electrode layer 34. The second substrate may have the same configuration as the first substrate, or may have a different configuration.

[0053] A-5. Method for Producing a Polymer-Dispersed Liquid Crystal Film The PDLC film can be produced by any suitable method. In one embodiment, the method for producing a PDLC film includes preparing a coating liquid containing a polymer matrix-forming resin, a liquid crystal compound (a photoreactive liquid crystal compound and, if present, a nonreactive 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 in the polymer matrix-forming resin to obtain a PDLC layer; and laminating a second substrate on the PDLC layer. The coating liquid is preferably an emulsion coating liquid in which liquid crystal particles containing a liquid crystal compound are dispersed in a dispersion medium. As the dispersion medium, water or a mixed solvent of water and a water-miscible organic solvent can be preferably used. Examples of water-miscible organic solvents include C1-3 alcohols, acetone, and DMSO.

[0054] In another embodiment, a method for producing a PDLC film includes preparing a coating solution containing a curable resin for forming a polymer matrix, a liquid crystal compound (a photoreactive liquid crystal compound and, if present, a nonreactive liquid crystal compound), and a polymerization initiator; applying the coating solution 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 and form a polymer matrix, thereby obtaining a PDLC layer. The coating solution is preferably in a homogeneous phase state, and phase separation between the polymer matrix and the liquid crystal compound can occur as the curable resin polymerizes. Ultraviolet light is preferably used as the active energy rays. Alternatively, the coating solution may be filled between the first and second substrates stacked via a spacer, followed by phase separation by irradiation with active energy rays.

[0055] A-6. Modifications FIG. 2 is a schematic cross-sectional view illustrating the configuration of a PDLC film according to another embodiment of the present invention. The PDLC film 100B has a PDLC layer 10 including a polymer matrix 12 and liquid crystal droplets 14 dispersed in the polymer matrix 12. The liquid crystal droplets 14 contain, as liquid crystal compounds, a photoreactive liquid crystal compound 15 having at least two reversible photodimerization functional groups and a nonreactive liquid crystal compound 16. The PDLC film 100B has 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 composed of substrate bodies 22 and 32, respectively, and do not have a transparent electrode layer. The PDLC film 100B having such a configuration can be preferably used, for example, as a diffusion film. The same explanations as above can be applied to the PDLC layer 10 and the substrate bodies 22 and 32. The PDLC film 100B can be manufactured by a method similar to that described in Section A-5.

[0056] B. Method of Using a Polymer-Dispersed Liquid Crystal Film According to another aspect of the present invention, a method of using the PDLC film described in Section A is provided. The method of using a PDLC film according to an embodiment of the present invention includes a fixation step in which a liquid crystal polymer is generated by a photodimerization reaction of a photoreactive liquid crystal compound, and a reset step in which the photoreactive liquid crystal compound is generated by a depolymerization reaction of the liquid crystal polymer. In the method of using a PDLC film according to an embodiment of the present invention, the fixation step can be performed again after the resetting step. The fixation and resetting steps may also be repeated. The number of repetitions is not limited as long as the effects of the present invention are achieved. The region in which the liquid crystal polymer is generated in the second or subsequent fixation step may be different from the region in which the liquid crystal polymer was generated in the previous fixation step. According to the method of use according to an embodiment of the present invention, the PDLC film described in Section A can be used as a rewritable PDLC film. Hereinafter, a method of using a PDLC film according to one embodiment of the present invention will be specifically described with reference to FIG. 3.

[0057] 3(a), a PDLC film 100A is prepared, which includes a PDLC layer 10 including a polymer matrix 12 and liquid crystal droplets 14 dispersed in the polymer matrix 12, and a first substrate 20 and a second substrate 30 disposed on either side of the PDLC layer 10. The liquid crystal droplets 14 include a photoreactive liquid crystal compound 15 having at least two reversible photodimerization functional groups. In the PDLC film 100A, the liquid crystal droplets 14 further include a non-reactive liquid crystal compound 16.

[0058] In the first fixing step, the PDLC film 100A is irradiated with light to promote the photodimerization reaction of the photoreactive liquid crystal compound 15 ( FIG. 3B ). This causes sequential polymerization of the photoreactive liquid crystal compound 15, resulting in the formation of a liquid crystal polymer 17 ( FIG. 3C ). In the illustrated example, light irradiation is performed through a photomask 200 with a predetermined pattern while a voltage is applied to the PDLC layer 10. This allows the photoreactive liquid crystal compound 15 in the irradiated region to be polymerized while oriented in the direction of the electric field. The generated liquid crystal polymer 17 does not have liquid crystallinity and is unresponsive to the electric field. Therefore, the liquid crystal polymer 17 is fixed in a state oriented in the thickness direction, and the orientation of the nonreactive liquid crystal compound 16 within the same liquid crystal droplet 14 is restricted by the liquid crystal polymer 17. As a result, the irradiated region remains transparent with low haze, both with and without applied voltage. On the other hand, in the non-irradiated region, the photodimerization reaction of the photoreactive liquid crystal compound 15 does not occur, so the liquid crystal polymer 17 is not formed, and the liquid crystal droplet 14 can change its refractive index depending on the applied voltage. As a result, the non-irradiated region is in a scattering state with high haze when no voltage is applied, and the haze decreases and becomes transparent when a voltage is applied. Therefore, according to the fixing process, by using a photomask corresponding to the desired pattern, it is possible to form a first region (irradiated region) and a second region (non-irradiated region) in a desired pattern, in which the amount of haze change differs between the applied and unapplied states. The amount of haze change in the first region between the applied and unapplied states is smaller than the amount of haze change in the second region.

[0059] The light irradiation conditions in the fixing step may be any conditions that cause a photodimerization reaction of the photoreactive liquid crystal compound, and the irradiation conditions, such as the wavelength, irradiation time, and irradiation temperature of the irradiation light, can be appropriately set depending on the type of the photoreactive liquid crystal compound, etc. When a photoreactive liquid crystal compound having an anthracene group as the photodimerization functional group is used, the peak wavelength of the irradiation light can be, for example, 315 nm to 400 nm, or, for example, 330 nm to 380 nm. The exposure dose can be, for example, 10 J / m ２ ~10,000 J / m ２ , and for example 100 J / m ２ ~5000 J / m２ The irradiation temperature can be, for example, from -20°C to 80°C, or from -20°C to 60°C.

[0060] Next, in the reset process, the PDLC film 100A is irradiated with light to promote the depolymerization reaction of the liquid crystal polymer 17 (FIG. 3(d)). This decomposes the liquid crystal polymer 17, generating photoreactive liquid crystal compounds 15 (FIG. 3(e)). In the illustrated example, the entire surface of the PDLC film 100A is irradiated with light, but it may also be irradiated only to the irradiated area. The reset process can erase the pattern applied to the PDLC film 100A. In the illustrated example, the entire pattern is erased and the PDLC film 100A is reset to its original state, but it may also be in a state where a portion of the liquid crystal polymer is depolymerized and the pattern is relaxed (the haze difference of the pattern is reduced). Furthermore, light irradiation may be performed under a voltage application state.

[0061] The light irradiation conditions in the resetting step may be any conditions that cause a depolymerization reaction of the liquid crystal polymer, and irradiation conditions such as the wavelength, irradiation time, and irradiation temperature of the irradiation light may be appropriately set depending on the type of photoreactive liquid crystal compound, etc. The peak wavelength of the irradiation light in the resetting step may be shorter than the peak wavelength of the irradiation light in the fixing step. When a photoreactive liquid crystal compound having an anthracene group as a photodimerization functional group is used, the peak wavelength of the irradiation light may be, for example, 230 nm to 290 nm, or, for example, 240 nm to 290 nm. The exposure dose may be, for example, 10 J / m ２ ~10,000 J / m ２ , and for example 100 J / m ２ ~5000 J / m ２ The irradiation temperature can be, for example, from -20°C to 80°C, or from -20°C to 60°C.

[0062] If necessary, a second fixing step can be performed after the resetting step. Specifically, the PDLC film 100A after the resetting step can be irradiated with light to promote the photodimerization reaction of the photoreactive liquid crystal compound 15. This causes the photoreactive liquid crystal compound 15 to undergo sequential polymerization, producing the liquid crystal polymer 17 (second fixing step). At this time, by performing light irradiation through a photomask with a different pattern from the photomask used in the first fixing step, a PDLC film having first and second regions in a different pattern from the pattern applied in the first fixing step can be obtained.

[0063] If necessary, after the second fixing step, another reset step can be performed (second reset step). The second reset step can erase the pattern formed in the second fixing step. As in the first reset step, the pattern may be completely erased, or may be relaxed (the haze difference of the pattern may be reduced).

[0064] 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 desired design.

[0065] In the embodiment shown in FIG. 3 , the photodimerization reaction of the photoreactive liquid crystal compound was allowed to proceed under a voltage application condition during the fixing step. However, as shown in FIG. 4 , the photodimerization reaction of the photoreactive liquid crystal compound may be allowed to proceed under no voltage application condition ( FIG. 4( b)). In this case, the photoreactive liquid crystal compound 15 in the irradiated region is polymerized and fixed in a non-oriented state, while the photoreactive liquid crystal compound 15 in the non-irradiated region does not undergo photodimerization. As a result, the irradiated region (first region) is in a scattering state with high haze both under and without voltage application, while the non-irradiated region (second region) is in a scattering state with high haze under no voltage application and becomes transparent upon voltage application. The amount of change in haze between the applied and unapplied states in the first region (irradiated region) is smaller than the amount of change in haze in the second region (non-irradiated region).

[0066] According to the above-described method for using a PDLC film, a patterned PDLC film can be obtained in which first and second regions are formed in a predetermined pattern, and the first and second regions have different amounts of haze change between the voltage-applied state and the voltage-unapplied state. 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 the present invention can be reversibly changed.

[0067] The method for using a PDLC film according to an embodiment of the present invention can also be applied to a PDLC film (diffusion film) 100B in which the substrate does not have a transparent electrode layer. For example, as shown in FIG. 5 , by alternately repeating the fixing process and resetting process described above on the PDLC film 100B, it is possible to form low-haze and high-haze regions of the PDLC film 100B in different patterns (patterns A and B in the illustrated example). In this case, the application of a voltage to the PDLC layer in the fixing process can be performed by placing separately prepared electrodes on the surfaces of the first substrate and the second substrate and applying a voltage to the electrodes.

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are by weight.

[0069] (1) Thickness: Measured using a digital micrometer (Anritsu Corporation, product name "KC-351C"). (2) Volume-average particle diameter of liquid crystal particles in liquid crystal emulsion: 0.1 wt % liquid crystal emulsion was added to 200 ml of an aqueous electrolyte solution (Coulter Corporation, "Isoton II"). The resulting mixture was used as a measurement sample using a Multisizer 3 (Coulter Corporation, aperture size = 20 μm). The volume of each particle diameter was measured by dividing the mixture into 256 equal logarithmic intervals from 0.4 μm to 12 μm, and the volume-average particle diameter was calculated by taking statistics of the volume for each particle diameter. Note that when particles of 12 μm or larger were present, the aperture size was changed to 30 μm, and the volume-average particle diameter was calculated by dividing the mixture into 256 equal logarithmic intervals from 0.6 μm to 18 μm. (3) Average particle diameter of resin particles: A measurement sample was prepared by adding a few drops of resin dispersion to 100 mL of water. A dynamic light scattering particle size distribution analyzer (Microtrac, product name "Nanotrac150") was used, and the measurement sample was placed in the measurement holder of the device, and after confirming on the monitor of the device that the concentration was measurable, the measurement was performed. (4) Haze A haze meter (Nippon Denshoku Co., Ltd., product name "NDH4000") was used to measure haze in accordance with JIS K 7136.

[0070] [Example 1] (First substrate and second substrate) An ITO layer was formed by sputtering on one surface of a PET substrate (thickness: 50 μm) to obtain a substrate having a structure of [substrate body / transparent electrode layer].

[0071] (Preparation of Coating Liquid) 2.5 parts of the photoreactive liquid crystal compound A shown below, 47 parts of a non-reactive liquid crystal compound (manufactured by JNC Corporation, product name "LX-153XX", birefringence Δn = 0.149), 49.5 parts of pure water, and 1.0 part of a surfactant (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") were mixed and treated with a homogenizer to prepare a liquid crystal emulsion. The average particle size of the liquid crystal particles in the obtained liquid crystal emulsion was 3.5 μm. An emulsion coating liquid was obtained by mixing 47.6 parts of the liquid crystal emulsion, 32 parts of an aqueous dispersion of polyether-based polyurethane resin (manufactured by DSM, product name "NeoRezR967", polymer average particle size: 80 nm, CV value = 0.27, solid content: 40 wt%), 0.1 part of a leveling agent (manufactured by DIC, product name "F-444"), 1 part of a crosslinking agent (tris[3-(2-methylaziridin-1-yl)propionic acid]=propylidinetrimethyl), and 19.3 parts of pure water.

[0072] (Production of PDLC Film) The emulsion coating liquid was applied to the ITO layer surface of the first substrate and dried at 40°C to form a 10 µm thick PDLC layer. Then, using a laminator, a lamination pressure of 0.4 MPa / m was applied, and a second substrate was laminated on the PDLC layer with the ITO layer facing the PDLC layer. This resulted in a PDLC film having a structure of [first substrate / PDLC layer / second substrate].

[0073] [Example 2] A PDLC film was obtained in the same manner as in Example 1, except that 1.25 parts of photoreactive liquid crystal compound B and 1.25 parts of photoreactive liquid crystal compound C shown below were used instead of 2.5 parts of photoreactive liquid crystal compound A.

[0074] Comparative Example 1 A liquid crystal emulsion was prepared by mixing 44.3 parts of a non-reactive liquid crystal compound (manufactured by JNC Corporation, product name "LX-153XX", birefringence Δn = 0.149), 4.9 parts of a polymerizable liquid crystal compound (manufactured by BASF Corporation, product name "PALIOCOLOR LC-242"), 0.3 parts of a photopolymerization initiator (manufactured by IGM, product name "OMNIRAD651"), 49.5 parts of pure water, and 1.0 part of a surfactant (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., "Noigen ET159") and treating with a homogenizer. The average particle size of the liquid crystal particles in the resulting liquid crystal emulsion was 3.5 μm. A PDLC film was obtained in the same manner as in Example 1, except that the liquid crystal emulsion obtained as described above was used.

[0075] The PDLC films obtained in the above Examples and Comparative Examples were subjected to the following fixing step, and then to the following reset step 1 or 2. The PDLC films that had been subjected to the reset step 2 were subjected to the following fixing step again. The PDLC films that had been subjected to the fixing step were left at room temperature without being subjected to the reset step, and used as control samples. [Fixing step] The PDLC films were irradiated with light (10 mW / m) with a peak wavelength of 365 nm, at a temperature of 25°C, with an AC voltage of 50 V applied to the PDLC layer. ２ [Resetting step 1] The PDLC film after the fixing step was irradiated with light (10 mW / m) having a peak wavelength of 280 nm. ２ [Reset Step 2] The PDLC film after the fixing step was irradiated with light (10 mW / m) having a peak wavelength of 265 nm. ２ ) was irradiated for 30 minutes.

[0076] FIG. 6 shows the change in haze when voltages of 0 V to 50 V were applied to the PDLC films of Examples 1 and 2 in the initial state (before the fixing step) and after the fixing step.

[0077] The haze of each PDLC film in the initial state and in each step with no voltage applied is shown in Table 1 and Fig. 7. Table 1 shows the haze of the PDLC film after the reset step 2 with no voltage applied.

[0078] As shown in Table 1 and Figures 6 and 7, in the PDLC film of the example, performing the fixing step with a voltage applied allowed the formation of a region that maintained a low haze even in the absence of a voltage, and performing the reset step after the fixing step allowed the haze in that region to be restored (increased) in the absence of a voltage. Furthermore, performing the fixing step a second time with a voltage applied allowed the formation of a region that maintained a low haze in the absence of a voltage. On the other hand, in the PDLC film of the comparative example, performing the fixing step with a voltage applied allowed the formation of a region that maintained a low haze in the absence of a voltage, but performing the reset step did not allow the haze in that region to be restored in the absence of a voltage.

[0079] The PDLC film of the present invention is suitable for various applications such as displays such as advertisements and guide boards, and smart windows.

[0080] 100 PDLC film 10 PDLC layer 12 Polymer matrix 14 Liquid crystal droplets 15 Photoreactive liquid crystal compound 16 Non-reactive liquid crystal compound 17 Liquid crystal polymer 20 First substrate 30 Second substrate

Claims

1. a polymer dispersed liquid crystal layer including a polymer matrix and droplets containing a liquid crystal compound dispersed in the polymer matrix; A polymer dispersed liquid crystal film, wherein the liquid crystal compound comprises a photoreactive liquid crystal compound having at least two reversible photodimerization functional groups.

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

3. 2. The polymer dispersed liquid crystal film of claim 1, wherein the reversible photodimerization functional group is selected from an anthracene group, a coumarin group, a cinnamic acid group, a stilbene group, and a thymine group.

4. 2. The polymer dispersed liquid crystal film according to claim 1, wherein the photoreactive liquid crystal compound comprises a photoreactive liquid crystal compound having three or more of the reversible photodimerization functional groups.

5. 2. The polymer dispersed liquid crystal film according to claim 1, further comprising substrates with transparent electrode layers disposed on both sides of the polymer dispersed liquid crystal layer.

6. 6. The polymer dispersed liquid crystal film according to claim 5, wherein the amount of change in haze between a voltage applied state and a voltage not applied state can be changed by a reversible photodimerization reaction of the photoreactive liquid crystal compound.

7. A method for using the polymer dispersed liquid crystal film according to claim 1, comprising: a fixing step of generating a liquid crystal polymer by a photodimerization reaction of the photoreactive liquid crystal compound; and a resetting step of generating the photoreactive liquid crystal compound by depolymerization of the liquid crystal polymer.

8. The method for using a polymer dispersed liquid crystal film according to claim 7 , wherein the fixing step is carried out again after the resetting step.

9. The method for using a polymer dispersed liquid crystal film according to claim 7 , wherein the fixing step and the resetting step are repeated.

10. 10. The method for using a polymer dispersed liquid crystal film according to claim 8, wherein the region where the liquid crystal polymer is produced in the second or subsequent fixing step is different from the region where the liquid crystal polymer is produced in the previous fixing step.