Dimming film, dimming device, and manufacturing method of dimming film

Abstract

The dimming sheet comprises: a dimming layer containing a liquid crystal composition; a pair of alignment layers sandwiching the dimming layer; and a pair of transparent electrode layers sandwiching the dimming layer and the pair of alignment layers. The thermal weight reduction rate of the alignment layer after heating at 130°C for 30 minutes is less than 4%. The alignment layer comprises a polymeric compound having a backbone composed of polyimide or a polyimide precursor. The alignment layer comprises a structure formed by reacting polyamic acid with a compound having at least one functional group selected from epoxy, carbodiimide, and oxazoline groups.

Description

Technical Field

[0001] This disclosure relates to dimming sheets, dimming devices, and methods for manufacturing dimming sheets. Background Technology

[0002] The dimming sheet includes a dimming layer comprising a liquid crystal composition and a pair of electrode sheets sandwiching the dimming layer. Each electrode sheet includes a transparent electrode layer facing the dimming layer and a transparent support layer supporting the transparent electrode layer on the side opposite to the dimming layer. A driving voltage is applied between the transparent electrode layers of the pair of electrode sheets. The orientation state of the liquid crystal compound in the dimming layer changes depending on whether a driving voltage is applied, thus enabling switching between a transparent state where light passes through the dimming layer and an opaque state where light transmission through the dimming layer is suppressed by scattering.

[0003] The dimming sheet is mounted on a transparent substrate such as a glass substrate. During this mounting process, high heat is sometimes applied to the dimming sheet. For example, the interlayer mounting technique involves heating the transparent substrates while holding the dimming sheet between two transparent substrates, thereby fixing the dimming sheet between the transparent substrates.

[0004] If high heat is applied to the dimming film, impurities are generated from the constituent layers of the dimming film. These impurities enter the dimming layer, which can sometimes reduce the reliability of properties such as the orientation control of the liquid crystal compound in the dimming layer. To address this problem, the dimming film in Patent Document 1 has a barrier surface treatment layer on the surface of the transparent support layer. This can suppress the intrusion of low-molecular-weight impurities generated from the resin-based transparent support layer due to hydrolysis and other processes into the dimming layer.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 6447757 Summary of the Invention

[0006] The problem that the invention aims to solve Furthermore, as a structure for a dimming disc, it is also known to have an alignment layer between the dimming layer and the transparent electrode layer. The alignment layer functions to control the orientation of the liquid crystal compound when no driving voltage is applied. Moreover, if high heat is applied to the dimming disc, impurities may sometimes be generated in the alignment layer. For example, if the polymer compound constituting the alignment layer has a polyimide backbone formed from polyamic acid, unreacted polyamic acid contained in the alignment layer may react upon heating, thereby generating H₂O as a low-molecular-weight impurity.

[0007] Unlike Patent Document 1, which addresses impurities generated from the transparent support layer, this case, where the primary cause is impurities generated from the alignment layer, cannot be solved by forming a surface treatment layer. This is because forming a surface treatment layer on the surface of the alignment layer would compromise the alignment layer's ability to control the alignment of the liquid crystal compound.

[0008] Therefore, countermeasures are needed to suppress the degradation of the dimming layer's characteristics caused by impurities generated from the alignment layer.

[0009] Methods for solving problems One method of a dimming sheet includes: a dimming layer comprising a liquid crystal composition; a pair of alignment layers sandwiching the dimming layer; and a pair of transparent electrode layers sandwiching the dimming layer and the pair of alignment layers, wherein the thermal weight reduction rate of the alignment layers is 4% or less when the alignment layers are heated at 130°C for 30 minutes.

[0010] One type of dimming device includes a dimming disc and a control unit that controls the application of a driving voltage to the dimming disc, thereby changing the haze of the dimming disc by applying the driving voltage.

[0011] One method of manufacturing a dimming film includes the steps of forming a first alignment layer on a first transparent electrode layer supported by a first transparent support layer, forming a second alignment layer on a second transparent electrode layer supported by a second transparent support layer, and forming a dimming layer comprising a liquid crystal composition between the first alignment layer and the second alignment layer, wherein the first alignment layer and the second alignment layer are formed such that the thermal weight reduction rate of the alignment layer is less than 4% when the alignment layer is heated at 130°C for 30 minutes. Attached Figure Description

[0012] Figure 1 This is a diagram illustrating the configuration of a dimming disc and a dimming device in one embodiment. Detailed Implementation

[0013] Referring to the accompanying drawings, one embodiment of the dimming plate, dimming device, and method for manufacturing the dimming plate will be described. Furthermore, the phrase "at least one of A and B" in this specification should be understood as meaning "only A, or only B, or both A and B".

[0014] [Composition of dimming discs and dimming devices] Reference Figure 1 The overall structure of the dimming plate and dimming device is explained.

[0015] like Figure 1As shown, the dimming film 10 includes a dimming layer 20, a first transparent electrode layer 31 and a second transparent electrode layer 32 as a pair of transparent electrode layers, a first transparent support layer 41 and a second transparent support layer 42 as a pair of transparent support layers, and a first alignment layer 51 and a second alignment layer 52 as a pair of alignment layers.

[0016] The dimming layer 20 is located between the first transparent electrode layer 31 and the second transparent electrode layer 32. The first transparent support layer 41 supports the first transparent electrode layer 31 on the side of the first transparent electrode layer 31 opposite to the dimming layer 20, and the second transparent support layer 42 supports the second transparent electrode layer 32 on the side of the second transparent electrode layer 32 opposite to the dimming layer 20.

[0017] Furthermore, the first alignment layer 51 is located between the dimming layer 20 and the first transparent electrode layer 31, and the first alignment layer 51 is in contact with both the dimming layer 20 and the first transparent electrode layer 31. The second alignment layer 52 is located between the dimming layer 20 and the second transparent electrode layer 32, and the second alignment layer 52 is in contact with both the dimming layer 20 and the second transparent electrode layer 32. That is, a pair of alignment layers sandwich the dimming layer 20, and a pair of transparent electrode layers sandwich the dimming layer 20 and the pair of alignment layers.

[0018] The dimming layer 20 comprises a transparent polymer layer and a liquid crystal composition. The transparent polymer layer has multiple voids, which are filled with the liquid crystal composition. The voids are spherical, ellipsoidal, or irregular in shape. The liquid crystal composition comprises a liquid crystal compound with negative dielectric anisotropy. That is, the dielectric constant of the liquid crystal compound is higher along its short axis than along its long axis.

[0019] The dimming layer 20 has any one of the following liquid crystal holding structures: polymer network type, polymer dispersion type, and capsule type. The polymer network type dimming layer 20 has a polymer network with a three-dimensional mesh structure. The polymer network is an example of a transparent polymer layer, and the liquid crystal composition is held in the interconnected mesh voids within the polymer network. The polymer dispersion type dimming layer 20 has a transparent polymer layer that defines a plurality of isolated voids, and the liquid crystal composition is held in the voids dispersed within the transparent polymer layer. The capsule type dimming layer 20 holds the liquid crystal composition in the voids within capsules dispersed within the transparent polymer layer.

[0020] The first transparent electrode layer 31 and the second transparent electrode layer 32 are both conductive and transparent to visible light. The materials of the transparent electrode layers 31 and 32 are, for example, indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, poly(3,4-ethylenedioxythiophene), silver alloy, etc.

[0021] The first transparent support layer 41 and the second transparent support layer 42 are both light-transparent substrates to the visible area. The materials of the transparent support layers 41 and 42 are, for example, synthetic resins or inorganic compounds. Synthetic resins include, for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polycarbonate, and polyolefins. Inorganic compounds include, for example, silicon dioxide, silicon oxynitride, and silicon nitride.

[0022] The transparent support layers 41 and 42 may have a surface treatment layer on their surface that has a barrier effect to inhibit the permeation of low molecular weight compounds. The surface treatment layer may be, for example, a photocurable resin film, a thermosetting resin film, or an inorganic oxide film.

[0023] The first alignment layer 51 and the second alignment layer 52 are both vertically aligned films that are light-transparent to the visible region. The first alignment layer 51 aligns the liquid crystal compound contained in the dimming layer 20 in such a way that the long axis direction of the liquid crystal compound is perpendicular to the surface of the first alignment layer 51 that is in contact with the dimming layer 20. The second alignment layer 52 aligns the liquid crystal compound contained in the dimming layer 20 in such a way that the long axis direction of the liquid crystal compound is perpendicular to the surface of the second alignment layer 52 that is in contact with the dimming layer 20.

[0024] A first connection portion 61 is disposed at the end of the first transparent electrode layer 31, which is used to electrically connect the first transparent electrode layer 31 to a control unit 60 that generates a voltage for driving the dimming disc 10. A second connection portion 62 is disposed at the end of the second transparent electrode layer 32 for electrically connecting the second transparent electrode layer 32 to the control unit 60.

[0025] The first connecting portion 61 and the second connecting portion 62 each, for example, include a conductive adhesive layer and a wiring substrate. The conductive adhesive layer is formed, for example, from anisotropic conductive film (ACF), anisotropic conductive paste (ACP), isotropic conductive film (ICF), or isotropic conductive paste (ICP). The wiring substrate is, for example, a flexible printed circuit board (FPC).

[0026] Alternatively, the first connecting part 61 and the second connecting part 62 may each have a structure in which a conductive material such as conductive tape is joined to a wire by brazing.

[0027] Transparent electrode layers 31 and 32 are connected to the control unit 60 via wiring extending from the connecting portions 61 and 62. The control unit 60 applies a voltage, i.e., a driving voltage, to the transparent electrode layers 31 and 32 through the connecting portions 61 and 62 to change the orientation state of the liquid crystal compound. By controlling whether a voltage is applied and controlling the magnitude of the applied voltage, the control unit 60 controls the potential difference between the transparent electrode layers 31 and 32. The dimming device is composed of the dimming disc 10, the control unit 60, and the connecting portions 61 and 62.

[0028] When no driving voltage is applied to the transparent electrode layers 31 and 32, the liquid crystal compound is aligned perpendicular to the surfaces of the alignment layers 51 and 52, i.e., along the thickness direction of the dimming layer 20, by the alignment restraint force of the alignment layers 51 and 52. As a result, light can easily pass through the dimming layer 20. Therefore, the dimming plate 10 is transparent when no driving voltage is applied.

[0029] When a driving voltage is applied to the transparent electrode layers 31 and 32, the liquid crystal compound is aligned perpendicular to the direction of the electric field, i.e., its long axis is parallel to the surfaces of the alignment layers 51 and 52. As a result, light incident on the dimming disc 10 is easily scattered in the dimming layer 20. Therefore, when the driving voltage is applied, the dimming disc 10 becomes opaque and appears whitish and cloudy. In the opaque state, the haze of the dimming disc 10 is greater than in the transparent state.

[0030] As described above, by switching the application and release of the driving voltage, the transparent state and the opaque state of the dimming plate 10 can be switched.

[0031] Furthermore, the dimming sheet 10 is adhered to a transparent substrate that is the object to which it is mounted. The transparent substrate is a glass substrate or a resin substrate. Examples of transparent substrates include window glass in moving vehicles, aircraft, etc., window glass installed in buildings, and partitions installed in vehicle interiors or rooms. The surface on which the dimming sheet 10 is adhered can be flat or curved. Alternatively, the dimming sheet 10 can be sandwiched between two transparent substrates. Furthermore, the opaque dimming sheet 10 can also be used as a screen for projected images.

[0032] [Materials for the dimming layer and alignment layer] The materials of the dimming layer 20 and the orientation layers 51 and 52 are described in detail.

[0033] The transparent polymer layer included in the dimming layer 20 is a cured product of a photopolymerizable compound. The photopolymerizable compound is compatible with the liquid crystal composition. The photopolymerizable compound can be an ultraviolet-curable compound or an electron beam-curable compound. When the photopolymerizable compound is an ultraviolet-curable compound, it can improve the dimensional control of the voids in the transparent polymer layer. The photopolymerizable compound can be one type of polymerizable compound or can contain two or more polymerizable compounds.

[0034] One example of a UV-curable compound is that it contains polymerizable unsaturated bonds at the ends of its molecular structure. Another example of a UV-curable compound is that it contains polymerizable unsaturated bonds outside the ends of its molecular structure. The UV-curable compound is at least one selected from acrylate compounds, methacrylate compounds, thiols, styrene compounds, and oligomers of these compounds. Acrylate compounds include diacrylate compounds, triacrylate compounds, and tetraacrylate compounds. Examples of acrylate compounds are butyl ethyl acrylate, ethylhexyl acrylate, and cyclohexyl acrylate. Methacrylate compounds include dimethacrylate compounds, trimethacrylate compounds, and tetramethacrylate compounds. Examples of methacrylate compounds are N,N-dimethylaminoethyl methacrylate, phenoxyethyl methacrylate, methoxyethyl methacrylate, and tetrahydrofurfuryl methacrylate. Examples of thiols are 1,3-propanedithiol and 1,6-hexanedithiol. Examples of styrene compounds are styrene and methylstyrene.

[0035] The liquid crystal composition contained in the dimming layer 20 comprises a liquid crystal compound with negative dielectric anisotropy. The liquid crystal compound is a non-polymerizable compound. The liquid crystal composition may contain one or more liquid crystal compounds.

[0036] The liquid crystal compound is selected from at least one of the following: Schiff base system, azo system, azo oxide system, biphenyl system, terphenyl system, benzoate system, diphenylacetylene system, pyrimidine system, pyridazine system, cyclohexane carboxylate system, phenylcyclohexane system, biphenylcyclohexane system, dicyanophenyl system, naphthalene system, and dioxane system.

[0037] Liquid crystal compounds are, for example, compounds shown in structural formulas (1-1) to (1-11) below. A liquid crystal composition may contain only one of the compounds shown in structural formulas (1-1) to (1-11) below, or it may contain two or more. In structural formulas (1-1) to (1-11) below, R... 1 and R 2 Each of the following is independently an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkenoxy group having 2 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms in which at least one hydrogen atom is replaced by fluorine or chlorine.

[0038] [Chemical Formula 1] [Chemical Formula 2] [Chemical Formula 3] [Chemical Formula 4] [Chemical Formula 5] [Chemical Formula 6] [Chemical Formula 7] [Chemical Formula 8] [Chemical Formula 9] [Chemical Formula 10] [Chemical Formula 11] If the liquid crystal compound is a compound with the above structural formulas (1-1) to (1-11), then the orientation control based on the orientation layers 51 and 52 containing the polymer compound described later can be accurately performed.

[0039] The ratio of the transparent polymer layer to the transparent polymer layer in the liquid crystal composition is preferably 20% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 60% by mass or less. When the ratio of the transparent polymer layer is within the above range, the size of the voids formed within the transparent polymer layer can be adequately ensured. Within the above range, a higher ratio of the transparent polymer layer improves the mechanical strength of the transparent polymer layer, while a lower ratio reduces the driving voltage of the dimming plate 10.

[0040] In addition to liquid crystal compounds, the liquid crystal composition may also contain dichroic pigments, viscosity reducers, defoamers, antioxidants, weathering agents, etc. If the liquid crystal composition contains dichroic pigments, it can make the opaque dimming sheet a color different from white. Examples of weathering agents are ultraviolet absorbers or light stabilizers. Furthermore, in addition to the transparent polymer layer and the liquid crystal composition, the dimming layer 20 may also contain spacers of a specified thickness. These spacers are, for example, bead spacers or photosensitive spacers, dispersed within the transparent polymer layer. The thickness of the dimming layer 20 is, for example, 10 μm or more and 30 μm or less.

[0041] Orientation layers 51 and 52 contain polymeric compounds. These polymeric compounds are, for example, polyimide-based polymers, polyamide-based polymers, acrylic polymers, polyester-based polymers, and polysiloxane-based polymers. Preferably, the main chain of these polymeric compounds has a backbone composed of polyimide or a polyimide precursor. The backbone composed of the polyimide precursor has the structure shown in the following general formula (2).

[0042] [Chemical Formula 12] In the above general formula (2), R 1 R represents a tetravalent organic group. 2 A represents a divalent organic group. 1 and A 2 Each independently represents an alkyl group having 1 to 8 hydrogen atoms or carbon atoms, A 3 and A 4 Each of the following groups independently represents any one of a hydrogen atom, an alkyl group with 1 to 5 carbon atoms, or an acetyl group with 1 to 5 carbon atoms, where n represents a positive integer. An example of a polyimide precursor is polyamic acid.

[0043] In the case where the orientation layers 51 and 52 contain a polymeric compound having a backbone composed of polyimide or a polyimide precursor, especially when the polymeric compound is a compound generated from polyamic acid, the polymeric compound preferably contains a structure generated by reacting polyamic acid with a compound having at least one functional group selected from epoxy, carbodiimide and oxazoline groups.

[0044] Hereinafter, compounds having at least one functional group selected from epoxy, carbodiimide and oxazoline are referred to as "specific compounds", and polymeric compounds containing structures generated by the reaction of polyamic acid with specific compounds are referred to as "specific polymeric compounds".

[0045] The specific compound can be a low-molecular-weight compound or a high-molecular-weight compound having the above-mentioned functional groups.

[0046] Various low-molecular-weight compounds with epoxy groups exist, among which compounds having functional groups that react with the material of the dimming layer 20 are preferred, as they improve the adhesion between the orientation layers 51, 52 and the dimming layer 20. Examples of such specific compounds include glycidyl acrylate, glycidyl methacrylate, methyl (3,4-epoxycyclohexyl) acrylate, allyl glycidyl ether, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene, vinyl ethylene oxide, and 4-vinyl-1,2-epoxycyclohexane.

[0047] Examples of high molecular weight compounds containing epoxy groups include copolymers containing glycidyl methacrylate. Commercially available examples include Marproof (Nippon Yusen) and the ARUFON UG-4000 series (Toa Synthetic).

[0048] Examples of low-molecular-weight compounds among specific compounds having an oxazoline group include 2-alkyl-2-oxazoline, 2-phenyl-2-oxazoline, 2,2'-bis(2-oxazoline), 2,2'-(1,4-phenylene)bis(2-oxazoline), etc.

[0049] High molecular weight compounds containing oxazoline groups are obtained by copolymerization of oxazoline-containing monomers. An example of a commercially available product is Epocros (Nippon Shokubai Corporation).

[0050] Examples of low-molecular-weight compounds among specific compounds having a carbodiimide group include N,N'-diisopropylcarbodiimide, N,N'-dicyclohexylcarbodiimide, N,N'-di-tert-butylcarbodiimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide.

[0051] High molecular weight compounds containing carbodiimide groups are obtained through the polycondensation of diisocyanates. Carbodilite (manufactured by Nisshinbo Chemical) is an example of a commercially available product.

[0052] When orientation layers 51 and 52 contain specific polymer compounds, they may contain unreacted specific compounds. The specific compounds contained in orientation layers 51 and 52 may be one type or more types.

[0053] Certain polymeric compounds can be manufactured using well-known methods for producing polyimides. Specifically, polyamic acid is generated by polymerizing a diamine compound with a tetracarboxylic acid, and then imidized by dehydration and cyclization of the polyamic acid, thereby obtaining a polymeric compound with a polyimide backbone. At this point, by adding a specific compound to the polyamic acid and carrying out an imidization reaction, the specific polymeric compound can be obtained.

[0054] [Manufacturing method of dimming film] The manufacturing method of the dimming film 10 will be described. First, a first sheet on which a first transparent electrode layer 31 is formed on a first transparent support layer 41 and a second sheet on which a second transparent electrode layer 32 is formed on a second transparent support layer 42 are prepared. The first transparent electrode layer 31 and the second transparent electrode layer 32 are formed by known thin film formation methods such as sputtering and vacuum evaporation.

[0055] Next, a first alignment layer 51 is formed on the first transparent electrode layer 31, and a second alignment layer 52 is formed on the second transparent electrode layer 32. The alignment layers 51 and 52 are formed by coating with an alignment layer coating solution to form a coating film and drying the coating film. The alignment layer coating solution used to form the alignment layers 51 and 52 containing a specific polymer compound includes polyamic acid, a specific compound, and a solvent.

[0056] The coating methods for orientation layer coating liquids can include well-known coating methods such as inkjet coating, gravure coating, spin coating, slot coating, rod coating, flexible coating, mold coating, dip coating, and roller coating.

[0057] The alignment layers 51 and 52 can be fired by drying the coating at a high temperature. The firing temperature is preferably above 100°C and below 200°C.

[0058] Next, a light-switching layer coating liquid containing the material of the light-switching layer 20 is generated. A coating film forming the light-switching layer 20 is formed by coating the light-switching layer coating liquid between the alignment layers 51 and 52 of the first and second sheets. The light-switching layer coating liquid contains at least a photopolymerizable compound, a liquid crystal composition, and a polymerization initiator. Examples of polymerization initiators include diketone compounds, acetophenone compounds, benzoin compounds, benzophenone compounds, and thioxanone compounds. The polymerization initiator can be a single compound or a combination of two or more compounds. Examples of polymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and cyclohexylphenyl ketone.

[0059] In the coating film formation process, a light-adjusting coating liquid is applied to the alignment layer of one of the first sheet and the second sheet to form a coating film, and the other of the first sheet and the second sheet is overlapped on the coating film, thereby forming a laminate containing the coating film sandwiched between the alignment layers of the first sheet and the second sheet.

[0060] The coating method for the dimming layer liquid can utilize well-known coating methods such as drop casting, inkjet printing, gravure coating, spin coating, slot coating, rod coating, flexible coating, mold coating, dip coating, and roller coating.

[0061] Next, the laminate is irradiated with light of a predetermined wavelength to initiate the polymerization reaction. The predetermined wavelength of light is an electron beam or ultraviolet light. The light can be directed towards the first sheet, the second sheet, or both. This causes the photopolymerizable compounds in the coating to polymerize, resulting in phase separation of the liquid crystal composition and the formation of the dimming layer 20.

[0062] Thus, a stack having a dimming layer 20, alignment layers 51, 52, transparent electrode layers 31, 32, and transparent support layers 41, 42 is formed. The stack is then shaped as needed to form a dimming sheet 10.

[0063] [Characteristics of dimming discs] In the dimming sheet 10, the thermogravimetric reduction rate of alignment layers 51 and 52 is less than 4%. The thermogravimetric reduction rate is the ratio of the weight reduction of alignment layers 51 and 52 after heating at 130°C for 30 minutes to the weight of alignment layers 51 and 52 before heating. Alignment layers 51 and 52 cut from the disassembled dimming sheet 10 are used as samples, and the thermogravimetric reduction rate is measured using a thermogravimetric measuring device.

[0064] If the thermal weight reduction rate of alignment layers 51 and 52 is less than 4%, impurities can be suppressed from escaping from alignment layers 51 and 52 even when high heat is applied to the dimming sheet 10. Therefore, it is possible to suppress the entry of impurities into the dimming layer 20 and thus prevent a decrease in the characteristics of the dimming layer 20. In particular, when the dimming sheet 10 is mounted between two glass substrates by means of an intermediate film with high temperature heating, the decrease in the characteristics of the dimming layer 20 can be suppressed.

[0065] Regarding the case where the alignment layers 51 and 52 contain polymeric compounds generated from polyamic acid, the relationship between the composition of the dimming film 10 and the rate of thermal weight reduction will be explained.

[0066] The following (Equation 1) is a reaction formula representing the formation reaction of polyimide from polyamic acid. In the following (Equation 1), R... 1 R represents a tetravalent organic group. 2 The radical represents a divalent organic group, and n represents a positive integer. By heating polyamic acid at high temperature, as shown in Formula 1 below, dehydration and cyclization occur in the polyamic acid, leading to imidization and the formation of polyimide.

[0067] [Chemical Formula 13] In the polyimide formation reaction, imidization is not limited to occurring in all repeating units of the polymer compound; repeating units of unimidized polyamic acid, i.e., unreacted repeating units, may also be included in the repeating units of the polymer compound contained in the alignment layers 51 and 52. In particular, when a highly flexible substrate is used in the transparent support layers 41 and 42 for purposes such as expanding applications and improving productivity, the firing temperature of the alignment layers 51 and 52 is limited to a lower temperature that suppresses thermal deformation of the transparent support layers 41 and 42, thus the imidization rate tends to be lower.

[0068] Furthermore, if high heat is applied to the manufactured dimming layer 10, imidization occurs in the unreacted repeating units, producing H2O as a reaction byproduct. If H2O enters the dimming layer 20, the orientation of the liquid crystal compound is disrupted, leading to a decrease in the optical properties of the dimming layer 20, such as haze.

[0069] In contrast, as described above, if the thermal weight reduction rate of the alignment layers 51 and 52 is less than 4%, the generation of H2O in the alignment layers 51 and 52 can be suppressed to the extent that the reduction of the optical properties of the dimming layer 20 is suppressed.

[0070] The rate of reduction in thermal weight can be controlled by at least one of the materials of the orientation layers 51 and 52 and the firing temperature.

[0071] By forming alignment layers 51 and 52 in a manner containing specific polymeric compounds, the rate of thermal weight loss can be reduced. At this time, alignment layers 51 and 52 are formed by firing a coating containing polyamic acid and the specific compound. During this process, imidization occurs in a portion of the repeating units of the polyamic acid, and in another portion of the repeating units, the epoxy, carbodiimide, or oxazoline groups present in the specific compound react with the carboxyl groups of the polyamic acid. As a result, even with a low imidization rate, the residue of unreacted repeating units containing carboxyl groups is reduced. Therefore, even when high heat is applied to the manufactured dimming sheet 10, the generation of H2O caused by the dehydration reaction can be suppressed, thus reducing the rate of thermal weight loss of alignment layers 51 and 52.

[0072] Furthermore, by increasing the firing temperature of alignment layers 51 and 52, the imidization rate can be increased. This reduces the number of unreacted repeating units in the polymer compounds contained in alignment layers 51 and 52. Therefore, even when high heat is applied to the manufactured dimming sheet 10, the generation of H2O can be suppressed, thus reducing the rate of thermal weight loss of alignment layers 51 and 52. Specifically, the firing temperature of alignment layers 51 and 52 is preferably 170°C or higher. Increasing the firing temperature to reduce the rate of thermal weight loss is particularly preferable when using materials with high heat resistance in the transparent support layers 41 and 42.

[0073] Furthermore, when a specific compound is used in the materials of the alignment layers 51 and 52, the rate of reduction in thermal weight can be kept below 4% even when the firing temperature of the alignment layers 51 and 52 is lowered. For example, the firing temperature can be below 150°C. If the firing temperature is low, materials that are easily deformed by heat can also be used for the transparent support layers 41 and 42, thus increasing the degree of freedom in the materials used for the transparent support layers 41 and 42.

[0074] On the other hand, if the firing temperature of the alignment layers 51 and 52 is increased, the thermal weight reduction rate can be reduced to less than 4% even if the materials of the alignment layers 51 and 52 do not use specific compounds. Therefore, the material cost of the alignment layers 51 and 52 can be reduced.

[0075] Furthermore, by selecting a material for the transparent polymer layer in such a way that the transparent polymer layer included in the dimming layer 20 becomes a dense film, it is also possible to suppress the entry of impurities generated in the alignment layers 51 and 52 into the dimming layer 20. If the dimming layer 20 in this embodiment adopts such a configuration, the reduction in the optical properties of the dimming layer 20 caused by impurities can be further suppressed. On the other hand, if the thermal weight reduction rate of the alignment layers 51 and 52 is 4% or less, the reduction in the optical properties of the dimming layer 20 caused by impurities can be suppressed regardless of the state of the transparent polymer layer film, thus increasing the degree of freedom in selecting the material of the transparent polymer layer.

[0076] Furthermore, even if the materials of the alignment layers 51 and 52 are different from the polymer compound generated from polyamic acid, if the thermal weight reduction rate of the alignment layers 51 and 52 is less than 4%, the mixing of impurities from the alignment layers 51 and 52 into the dimming layer 20 can be appropriately suppressed. Therefore, the reduction in the properties of the dimming layer 20 can be suppressed.

[0077] [Example] The above-described dimming film will be described using specific embodiments and comparative examples.

[0078] (The formation of polyamic acid solution) <Materials> The following describes the diamine compound and tetracarboxylic acid component used in the synthesis of polyamic acid.

[0079] • Diamine compound B1: 4,4'-Diaminodiphenylmethane (manufactured by Tokyo Chemical Industry) • Diamine compound B2: 3,5-Diaminobenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Tetracarboxylic acid dianhydride C1:3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (manufactured by Tokyo Chemical Industry) • Tetracarboxylic dianhydride C2: 1,2,3,4-cyclobutanetetracarboxylic dianhydride (manufactured by Tokyo Chemical Industry) <Manufacturing Method> As a first step, diamine compounds B1 and B2 and tetracarboxylic acid dianhydride C1 are mixed in N-ethyl-2-pyrrolidone (NEP) as a solvent in the following proportions and reacted at 80°C for 5 hours to generate a first reaction solution. Furthermore, the following descriptions of materials in parts by weight indicate the relative weight ratios of the materials used in the first and second steps.

[0080] B1: 10 parts by weight B2: 8 parts by weight C1: 4 parts by weight NEP: 75 servings by weight As a second step, tetracarboxylic acid dianhydride C2 and NEP are added to the first reaction solution in the following proportions, and the reaction is carried out at 40°C for 6 hours. This yields a polyamic acid solution. The concentration of the resin solids in the polyamic acid solution is 25% by mass.

[0081] C2: 16 parts by weight NEP: 38 servings by weight (Generation of the orientation layer coating solution) Using the above-mentioned polyamic acid solution as the first component, the first component, the second component, NEP as a solvent, and butyl cellosolve are mixed in the following proportions and stirred at 50°C for 24 hours to generate a coating solution for forming an orientation layer, namely, an orientation layer coating solution. Furthermore, the following descriptions of materials in parts by weight indicate the relative weight ratios of the materials used to generate the orientation layer coating solution.

[0082] First component (polyamic acid solution): 16 parts by weight Second ingredient: 1 part by weight NEP: 36 servings by weight Butyl cellosolve: 48 parts by weight The following describes compounds used as the second component.

[0083] Compound A1: Glycidyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) Compound A2: Methyl (3,4-epoxycyclohexyl) acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) Compound A3: An epoxy-containing acrylic polymer (Marproof G-0150M, manufactured by Nippon Oil). Compound A4: Oxazoline-containing polystyrene (Epocros RPS-1005, Nippon Shokubai Corporation) • Compound A5: A polymer containing carbodiimide groups (Carbodilite V-02B, manufactured by Nisshinbo Chemical). Compound A6: A condensation product of pentaerythritol and acrylic acid (Viscoat #300, manufactured by Osaka Organic Chemical Industry). In the second component, compounds A1, A2, and A3 have epoxy groups, compound A4 has an oxazoline group, and compound A5 has a carbodiimide group. That is, compounds A1, A2, A3, A4, and A5 are specific compounds. Compound A6 has a hydroxyl group.

[0084] (Generation of the light-adjusting coating liquid) A liquid crystal compound, a photopolymerizable compound, a polymerization initiator, and a spacer are mixed to generate a coating solution for forming a dimming layer, namely, a dimming layer coating solution. Two coating solutions with different compositions are generated as dimming layer coating solutions. Details of the materials in each coating solution and their mixing ratios are described below. Furthermore, the following descriptions of materials in parts by weight indicate the relative weight ratios of the materials used to generate the dimming layer coating solutions.

[0085] <Coating Solution I> • Liquid crystal composition: 50 parts by weight of fluorine-based nematic mixed liquid crystal (MLC-6608, Merck) Photopolymerizable compounds: Isoborneol acrylate (A-IB, manufactured by Osaka Organic Chemical Industry) 36 parts by weight 10 parts by weight of ethoxylated trimethylolpropane triacrylate (AT-20, manufactured by Shin-Nakamura Chemical Industry) Pentaerythritol tetra(3-mercaptobutyrate) (Karenz MT PE-1, manufactured by Showa Denko) 2 parts by weight • Polymerization initiator: 1 part by weight of 1-hydroxycyclohexylphenyl ketone (prepared by IGM Resins BV) • Spacer: 1 part by weight of divinylbenzene spherical particles (manufactured by Sekisui Chemicals Co., Ltd., particle size 10 μm) Furthermore, the aforementioned liquid crystal composition is a nematic liquid crystal, comprising two liquid crystal compounds with negative dielectric anisotropy. The refractive index anisotropy of the mixture of the two liquid crystal compounds is also present. n is 0.20.

[0086] <Coating II> • Liquid crystal composition: 50 parts by weight of fluorine-based nematic mixed liquid crystal (MLC-6608, Merck) Photopolymerizable compounds: Isoborneol acrylate (A-IB, manufactured by Osaka Organic Chemical Industry) 36 parts by weight Pentaerythritol tetraacrylate (A-TMMT, manufactured by Shin-Nakamura Chemical Industry) 5 parts by weight 5 parts by weight of ethoxylated polyethylene glycol acrylate (Light Acrylate 14EGA, manufactured by Kyoei Chemicals). Pentaerythritol tetra(3-mercaptobutyrate) (Karenz MT PE-1, manufactured by Showa Denko) 2 parts by weight • Polymerization initiator: 1 part by weight of 1-hydroxycyclohexylphenyl ketone (prepared by IGM Resins BV) • Spacer: 1 part by weight of divinylbenzene spherical particles (manufactured by Sekisui Chemicals Co., Ltd., particle size 10 μm) Furthermore, the aforementioned liquid crystal composition is a nematic liquid crystal, comprising two liquid crystal compounds with negative dielectric anisotropy. The refractive index anisotropy of the mixture of the two liquid crystal compounds is also present. n is 0.20.

[0087] (The formation of a dimming plate) A first sheet is fabricated as a laminate of the first transparent support layer and the first transparent electrode layer by sputtering to form a first transparent electrode layer. Similarly, a second sheet is fabricated as a laminate of the second transparent support layer and the second transparent electrode layer by sputtering to form a second transparent electrode layer. The first and second transparent support layers are each made of polyethylene terephthalate and have a thickness of 125 μm. The first and second transparent electrode layers are each made of indium tin oxide and have a thickness of 30 nm.

[0088] Next, an alignment layer coating solution was applied to the transparent electrode layers of the first and second sheets using a rod coater to form a coating film. Then, the coating film was fired by heating and drying for 4 minutes to form an alignment layer. The thickness of each alignment layer was 100 nm.

[0089] Next, a dimming layer coating is dropwise added to the alignment layer on the first sheet, sandwiching a coating film composed of the dimming layer coating between the alignment layers of the first and second sheets to obtain a laminate formed by bonding the first and second sheets. The thickness of the coating film is 10 μm. By irradiating the first transparent support layer of the laminate with 365 nm ultraviolet light, a dimming layer is formed, resulting in a dimming film. The intensity of the ultraviolet light is 8 mW / cm². 2 The ultraviolet radiation exposure time was 120 seconds.

[0090] (Structure of Examples, Comparative Examples, and Reference Examples) By using the materials and processes described above, at least one of the following was made different: whether or not a second component was added to the alignment layer coating solution, the compound used as the second component, the coating solution used as the dimming layer coating solution, and the firing temperature of the alignment layer, thereby obtaining dimming sheets of Examples 1 to 8, Comparative Examples 1 and 2, and Reference Examples.

[0091] (evaluate) <Reduction in thermal weight> The alignment layer was cut from the dimming plate using a clean cutter, and the weight loss rate was measured when the alignment layer was heated at 130°C for 30 minutes under a nitrogen atmosphere. In the determination of the thermogravimetric analysis (TGA) rate, a differential thermal gravimetric analyzer (STA7200RV, Hitachi High-Tech Science) was used, and the sample was weighed in an aluminum dish.

[0092] <Haze> The haze of the dimming sheet was measured in its transparent state before and after the heat resistance test. The transparent state was defined as the state in which no AC voltage was applied between the transparent electrode layers, i.e., no potential difference was generated between the transparent electrode layers. Haze was measured according to JIS K 7136:2000. In the heat resistance test, the dimming sheet was heated at 130°C for 30 minutes in an oven.

[0093] In the evaluation of haze, a haze level of less than 10% is designated as good ("S"), and a haze level of more than 10% is designated as bad ("F").

[0094] (Evaluation Results) Table 1 shows the results of the above evaluation items regarding the examples, comparative examples, and reference examples, including whether a second component was added to the alignment layer coating liquid, the compound used as the second component, the coating liquid used as the light-adjusting layer coating liquid, the firing temperature of the alignment layer, and the results of each of the above evaluation items.

[0095] As shown in Table 1, in Examples 1-8 where the thermal weight reduction rate of the alignment layer was less than 4%, the haze of the transparent dimming film after the heat resistance test was less than 10%, and the difference from the initial haze before the heat resistance test was also small. Therefore, it can be said that the reduction in optical properties caused by high-temperature heating was suppressed in Examples 1-8, and good optical properties were obtained after the heat resistance test.

[0096] On the other hand, in Comparative Examples 1 and 2, where the thermal weight reduction rate of the alignment layer exceeded 4%, the haze of the transparent dimming film after the heat resistance test increased to more than 10%, and the reduction in optical properties caused by high temperature heating was significant.

[0097] In Examples 1-8 and Comparative Examples 1 and 2, a specific compound was added as a second component to the alignment layer coating solution in Examples 1-6. On the other hand, no second component was added to the alignment layer coating solution in Comparative Example 1, and a compound different from the specific compound was added as a second component to the alignment layer coating solution in Comparative Example 2. The firing temperatures of the alignment layers in Examples 1-6 and Comparative Examples 1 and 2 were all the same low temperature. Therefore, it can be shown that by adding a specific compound to the alignment layer coating solution, the rate of decrease in thermal weight can be reduced.

[0098] Furthermore, in Examples 7 and 8, no specific compound was added to the orientation layer coating solution, but the firing temperature of the orientation layer was a high temperature of 170°C or higher. Therefore, it can be shown that by setting the firing temperature to a high temperature, the rate of decrease in thermal weight can also be reduced.

[0099] Furthermore, in the reference example, no specific compound was added to the alignment layer coating solution, and the firing temperature was low. The thermal weight reduction rate of the alignment layer exceeded 4%, but the reduction in optical properties caused by high-temperature heating was suppressed. The dimming layer coating solution used in the reference example contains monomers with small double bond equivalents, thereby forming a dense transparent polymer layer of the dimming layer. As a result, even if impurities are generated in the alignment layer through high-temperature heating, the intrusion of impurities into the dimming layer is suppressed.

[0100] As in Example 6, if the thermal weight reduction rate of the alignment layer is 4% or less and the dimming layer coating contains monomers with a small double bond equivalent, the reduction in optical properties caused by high-temperature heating can be further suppressed. On the other hand, as in Examples 1-5, 7, and 8, even if the density of the transparent polymer layer of the dimming layer is not high, as long as the thermal weight reduction rate of the alignment layer is 4% or less, the reduction in optical properties caused by high-temperature heating can be sufficiently suppressed, thus allowing for a high degree of freedom in the material of the dimming layer.

[0101] As described above in the embodiments and examples, the following effects can be obtained by using the dimming film.

[0102] (1) The heat weight reduction rate when the alignment layer is heated at 130°C for 30 minutes is less than 4%. Therefore, even when high heat is applied to the dimming film, the generation of impurities in the alignment layer can be suppressed, thus suppressing the reduction in properties caused by the intrusion of impurities into the dimming layer.

[0103] (2) If the orientation layer contains a polymeric compound having a backbone of polyimide or polyimide precursor, an orientation layer with orientation control function of liquid crystal compound can be appropriately realized.

[0104] (3) The polymeric compound contained in the orientation layer comprises a structure formed by the reaction of polyamic acid with a compound having at least one functional group selected from epoxy, carbodiimide and oxazolinyl. In addition, the orientation layer comprises a compound having at least one functional group selected from epoxy, carbodiimide and oxazolinyl.

[0105] Based on the above structure, the inclusion of unreacted polyamic acid structures with carboxyl groups in the polymer compound can be suppressed. Therefore, the generation of water as an impurity due to dehydration reaction during high-temperature heating can be suppressed. Thus, an orientation layer with a thermal weight loss rate of less than 4% can be accurately achieved.

[0106] (4) The specific compound having an epoxy group comprises at least one selected from glycidyl acrylate, glycidyl methacrylate, methyl (3,4-epoxycyclohexyl) acrylate, allyl glycidyl ether, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene, vinyl ethylene oxide, 4-vinyl-1,2-epoxycyclohexane, and copolymers containing glycidyl methacrylate. Based on the above configuration, an orientation layer with a heat weight reduction rate of less than 4% can be accurately achieved.

[0107] (5) The specific compound having an oxazoline group comprises at least one selected from 2-alkyl-2-oxazoline, 2-phenyl-2-oxazoline, 2,2'-bis(2-oxazoline), 2,2'-(1,4-phenylene)bis(2-oxazoline), and copolymers containing oxazoline monomers. Based on the above configuration, an orientation layer with a thermal weight reduction rate of less than 4% can be accurately achieved.

[0108] (6) The specific compound having a carbodiimide group includes at least one selected from the condensation polymers of N,N'-diisopropylcarbodiimide, N,N'-dicyclohexylcarbodiimide, N,N'-di-tert-butylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and diisocyanates. Based on the above configuration, an orientation layer with a thermal weight reduction rate of 4% or less can be accurately achieved.

[0109] (7) The firing temperature of the orientation layer is set to a high temperature so that the thermal weight reduction rate is less than 4%. Thus, an orientation layer with a thermal weight reduction rate of less than 4% can be accurately achieved.

[0110] (8) The alignment layer is formed by firing a coating containing polyamic acid and a specific compound at a firing temperature of 150°C or below. This suppresses the formation of impurities in the alignment layer, and the low firing temperature allows the use of materials that are easily deformed by heat in the transparent support layer. Therefore, the material flexibility of the transparent support layer can be improved.

Claims

1. A dimming film, comprising: A dimming layer comprising a liquid crystal composition; A pair of alignment layers holding the dimming layer; and A pair of transparent electrode layers sandwiching the dimming layer and the pair of alignment layers. in, The thermal weight reduction rate of the alignment layer when heated at 130°C for 30 minutes is less than 4%.

2. The dimming film according to claim 1, wherein, The orientation layer comprises a polymeric compound having a backbone composed of polyimide or a polyimide precursor, the backbone being composed of the polyimide precursor having the structure shown in the following general formula (2). In general formula (2), R 1 R represents a tetravalent organic group. 2 A represents a divalent organic group. 1 and A 2 Each independently represents an alkyl group having 1 to 8 hydrogen atoms or carbon atoms. A 3 and A 4 Each of the following groups can be independently represented: a hydrogen atom, an alkyl group with 1 to 5 carbon atoms, or an acetyl group with 1 to 5 carbon atoms, where n represents a positive integer.

3. The dimming film according to claim 2, wherein, The polymeric compound comprises a structure generated by the reaction of polyamic acid with a specific compound, wherein the specific compound is a compound having at least one functional group selected from epoxy, carbodiimide and oxazoline.

4. The dimming film according to claim 3, wherein, The specific compound having an epoxy group comprises at least one selected from glycidyl acrylate, glycidyl methacrylate, methyl (3,4-epoxycyclohexyl) acrylate, allyl glycidyl ether, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene, vinyl ethylene oxide, 4-vinyl-1,2-epoxycyclohexane, and copolymers containing glycidyl methacrylate.

5. The dimming film according to claim 3, wherein, The specific compound having an oxazoline group comprises at least one selected from 2-alkyl-2-oxazoline, 2-phenyl-2-oxazoline, 2,2'-bis(2-oxazoline), 2,2'-(1,4-phenylene)bis(2-oxazoline), and copolymers containing oxazoline monomers.

6. The dimming film according to claim 3, wherein, The specific compound having a carbodiimide group comprises at least one selected from the condensation polymers of N,N'-diisopropylcarbodiimide, N,N'-dicyclohexylcarbodiimide, N,N'-di-tert-butylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and diisocyanates.

7. The dimming film according to claim 2, wherein, The orientation layer contains a specific compound having at least one functional group selected from epoxy, carbodiimide, and oxazoline.

8. The dimming film according to claim 7, wherein, The specific compound having an epoxy group comprises at least one selected from glycidyl acrylate, glycidyl methacrylate, methyl (3,4-epoxycyclohexyl) acrylate, allyl glycidyl ether, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene, vinyl ethylene oxide, 4-vinyl-1,2-epoxycyclohexane, and copolymers containing glycidyl methacrylate.

9. The dimming film according to claim 7, wherein, The specific compound having an oxazoline group comprises at least one selected from 2-alkyl-2-oxazoline, 2-phenyl-2-oxazoline, 2,2'-bis(2-oxazoline), 2,2'-(1,4-phenylene)bis(2-oxazoline), and copolymers containing oxazoline monomers.

10. The dimming film according to claim 7, wherein, The specific compound having a carbodiimide group comprises at least one selected from the condensation polymers of N,N'-diisopropylcarbodiimide, N,N'-dicyclohexylcarbodiimide, N,N'-di-tert-butylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and diisocyanates.

11. The dimming film according to claim 1, wherein, The dimming layer comprises a transparent polymer layer containing multiple voids. The liquid crystal composition fills the voids. The proportion of the transparent polymer layer in the transparent polymer layer and the transparent polymer layer in the liquid crystal composition is more than 20% by mass and less than 80% by mass.

12. A dimming device comprising: The dimming film according to any one of claims 1 to 11; and The control unit controls the application of the driving voltage to the dimming plate. in, The haze of the dimming plate is changed by applying the driving voltage.

13. A method for manufacturing a dimming film, comprising: The steps of forming a first alignment layer on a first transparent electrode layer supported by a first transparent support layer and forming a second alignment layer on a second transparent electrode layer supported by a second transparent support layer; and The step of forming a dimming layer comprising a liquid crystal composition between the first alignment layer and the second alignment layer. in, The first orientation layer and the second orientation layer are formed such that the thermal weight reduction rate of the orientation layer is less than 4% when the orientation layer is heated at 130°C for 30 minutes.

14. The method for manufacturing a dimming film according to claim 13, wherein, The steps of forming the first alignment layer and the second alignment layer include firing the coating film to form each alignment layer. The firing temperature is set such that the heat weight reduction rate is less than 4%.

15. The method for manufacturing a dimming film according to claim 13, wherein, The steps of forming the first orientation layer and the second orientation layer include firing the coating film to form each orientation layer, the coating film comprising polyamic acid and a compound having at least one functional group selected from epoxy, carbodiimide, and oxazoline groups. The firing temperature is below 150°C.

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